Low density aerospace compositions and sealants

ABSTRACT

Low density aerospace compositions and sealants are disclosed. The low density compositions and sealants are characterized by a high volume percent loading of low density microcapsules.

This application is a continuation of U.S. application Ser. No.16/354,338 filed on Mar. 15, 2019, now allowed, which is a continuationof U.S. application Ser. No. 15/420,138, filed on Jan. 31, 2017, whichissued as U.S. Pat. No. 10,280,348, each of which is incorporated byreference in its entirety.

FIELD

The present disclosure relates to low density compositions and sealants.The compositions and sealants are characterized by a high volume percentloading of low density microcapsules.

BACKGROUND

Aerospace sealants must satisfy demanding mechanical, chemical, andenvironmental requirements. The sealants can be applied to a variety ofsurfaces including metal surfaces, primer coatings, intermediatecoatings, finished coatings, and aged coatings. Sealants comprisingsulfur-containing prepolymers that exhibit acceptable fuel resistance,thermal resistance, and flexibility for aerospace applications aredescribed, for example, in U.S. Pat. No. 6,172,179. In sealants such asthose described in U.S. Application Publication Nos. 2006/0270796,2007/0287810, and 2009/0326167, a sulfur-containing polymer such as athiol-terminated polythioether prepolymer can be reacted with apolyepoxide curing agent in the presence of an amine catalyst to providea cured product. These systems are useful as sealants and can meet thedemanding performance requirements of the aerospace industry includingfuel resistance. Cured aerospace sealants must exhibit acceptabletensile strength, elongation, and adhesion to a variety of aerospacesubstrates and must maintain these properties following exposure toaviation fluids.

Reducing the weight of aerospace components including coatings andsealants can significantly increase fuel economy. To reduce the weightof aerospace vehicles low density filler can be added to a coatingcomposition. Coatings and sealants having a specific gravity of about 1are commercially available. To further reduce the weight of aerospacevehicles it is desirable that coatings and sealants have a specificgravity less than 1.

U.S. Pat. Nos. 8,816,023 and 8,993,691, each of which is incorporated byreference in its entirety, disclose low density aerospace sealantcompositions characterized by a specific gravity of about 1. Thesecompositions include low density filler formed from thermally expandablethermoplastic microcapsules that have an exterior coating of anaminoplast resin functionalized with a polythiol. Cured compositionscomprising the thiol-functionalized coated microcapsules exhibitedsuperior solvent resistance as determined by percentage swellmeasurements following immersion in methyl ethyl ketone or in JetReference Fuel (JRF) Type I for 7 days at 140° F. (60° C.) compared tolightweight sealants made using thermally expandable thermoplasticmicrocapsules without the polythiol-functionalized aminoplast resincoating. Other important properties such as tensile strength,elongation, and adhesion following immersion in JRF Type I and/or NaClwere not evaluated. The sealant compositions disclosed in U.S. Pat. Nos.8,816,023 and 8,993,691 were limited to compositions having a specificgravity of about 1 and a loading of low density microcapsules of about30 vol %, where vol % is based on the total volume of the sealantcomposition or about 2 wt % where wt % is based on the total weight ofthe composition.

Increasing the loading of light weight fillers can reduce the propertiesof a cured sealant. For example, the cohesion strength of a sealant isprimarily imparted by the resins, and as the vol % of a fillerincreases, for example, to 50 vol % of the composition, there is lessresin available to support the physical properties of the cured sealant.Also, with increasing filler content, the interface between the fillerparticles and the binder increases and can provide additional failuresites. The binder and additives must impart sufficient integrity for thesealant to adhere to both the surface of the substrate and to theincorporated filler particles.

Therefore, it is desirable to provide low density sealants having aspecific gravity less than 0.9 that meet aerospace sealant performancerequirements.

SUMMARY

According to the present invention, a composition comprises: from 50 wt% to 70 wt % of a thiol-terminated polythioether prepolymer; from 15 wt% to 21 wt % of a polyepoxide; and from 35 vol % to 55 vol % of a lowdensity filler, wherein the low density filler is characterized by aspecific gravity less than 0.1, and the low density filler comprises lowdensity microcapsules comprising a coating of an aminoplast resin;wherein wt % is based on the total weight of the composition, and vol %is based on the total volume of the composition, and wherein thecomposition is characterized by a specific gravity less than 0.9,wherein the specific gravity is determined according to ASTM D1475(modified).

According the present invention, a cured sealant is prepared using acomposition according to the present invention.

According the present invention, a part comprises a cured sealantaccording to the present invention.

According the present invention, a method of sealing a part, comprises:applying a composition according to the present invention to at leastone surface of a part; and curing the applied composition to seal thepart.

According the present invention, a sealant system comprises a firstcomponent and a second component, wherein, the first componentcomprises: from 50 wt % to 70 wt % of a thiol-terminated polythioether;from 2.5 wt % to 4.0 wt % of a low density filler, wherein the lowdensity filler is characterized by a specific gravity within a rangefrom 0.01 to 0.09, and the low density filler comprises low densitymicrocapsules comprising a coating of an aminoplast resin, wherein thespecific gravity is determined according to ASTM D1475, wherein wt % isbased on the total weight of the first component; and the secondcomponent comprises: from 75 wt % to 95 wt % of a poly epoxide, whereinwt % is based on the total weight of the second component, wherein thefirst component and the second component combined provide thecomposition according to the present invention.

According the present invention, a cured sealant is prepared using asystem according to the present invention.

According the present invention, a part comprises a cured sealantprepared using a system according the present invention.

According the present invention, method of sealing a part, comprises:combining the first component and the second component of a sealantsystem according to the present invention to provide a curable sealantcomposition; applying the curable sealant composition to at least onesurface of a part; and curing the applied curable sealant composition toseal the part.

DETAILED DESCRIPTION

For purposes of the following detailed description, it is to beunderstood that embodiments provided by the present disclosure mayassume various alternative variations and step sequences, except whereexpressly specified to the contrary. Moreover, other than in anyoperating examples, or where otherwise indicated, all numbersexpressing, for example, quantities of ingredients used in thespecification and claims are to be understood as being modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the followingspecification and attached claims are approximations that may varydepending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard variation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

A dash (“-”) that is not between two letters or symbols is used toindicate a point of bonding for a substituent or between two atoms. Forexample, —CONH₂ is attached through the carbon atom.

“Alkanediyl” refers to a diradical of a saturated, branched orstraight-chain, acyclic hydrocarbon group, having, for example, from 1to 18 carbon atoms (C₁₋₁₈), from 1 to 14 carbon atoms (C₁₋₁₄), from 1 to6 carbon atoms (C₁₋₆), from 1 to 4 carbon atoms (C₁₋₄), or from 1 to 3hydrocarbon atoms (C₁₋₃). It will be appreciated that a branchedalkanediyl has a minimum of three carbon atoms. An alkanediyl can beC₂₋₁₄ alkanediyl, C₂₋₁₀ alkanediyl, C₂₋₈ alkanediyl, C₂₋₆ alkanediyl,C₂₋₄ alkanediyl, or C₂₋₃ alkanediyl. Examples of alkanediyl groupsinclude methane-diyl (—CH₂—), ethane-1,2-diyl (—CH₂CH₂—),propane-1,3-diyl and iso-propane-1,2-diyl (e.g., —CH₂CH₂CH₂— and—CH(CH₃)CH₂—), butane-1,4-diyl (—CH₂CH₂CH₂CH₂—), pentane-1,5-diyl(—CH₂CH₂CH₂CH₂CH₂—), hexane-1,6-diyl (—CH₂CH₂CH₂CH₂CH₂CH₂—),heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl, decane-1,10-diyl,and dodecane-1,12-diyl.

“Alkanecycloalkane” refers to a saturated hydrocarbon group having oneor more cycloalkyl and/or cycloalkanediyl groups and one or more alkyland/or alkanediyl groups, where cycloalkyl, cycloalkanediyl, alkyl, andalkanediyl are defined herein. Each cycloalkyl and/or cycloalkanediylgroup(s) can be C₃₋₆, C₅₋₆, cyclohexyl or cyclohexanediyl. Each alkyland/or alkanediyl group(s) can be C₁₋₆, C₁₋₄, C₁₋₃, methyl, methanediyl,ethyl, or ethane-1,2-diyl. An alkanecycloalkane group can be C₄₋₁₈alkanecycloalkane, C₄₋₁₆ alkanecycloalkane, C₄₋₁₂ alkanecycloalkane,C₄₋₈ alkanecycloalkane, C₆₋₁₂ alkanecycloalkane, C₆₋₁₀alkanecycloalkane, or C₆₋₉ alkanecycloalkane. Examples ofalkanecycloalkane groups include 1,1,3,3-tetramethylcyclohexane andcyclohexylmethane.

“Alkanecycloalkanediyl” refers to a diradical of an alkanecycloalkanegroup. An alkanecycloalkanediyl group can be C₄₋₁₈alkanecycloalkanediyl, C₄₋₁₆ alkanecycloalkanediyl, C₄₋₁₂alkanecycloalkanediyl, C₄₋₈ alkanecycloalkanediyl, C₆₋₁₂alkanecycloalkanediyl, C₆₋₁₀ alkanecycloalkanediyl, or C₆₋₉alkanecycloalkanediyl. Examples of alkanecycloalkanediyl groups include1,1,3,3-tetramethylcyclohexane-1,5-diyl and cyclohexylmethane-4,4′-diyl.

“Alkyl” refers to a monoradical of a saturated, branched orstraight-chain, acyclic hydrocarbon group having, for example, from 1 to20 carbon atoms, from 1 to 10 carbon atoms, from 1 to 6 carbon atoms,from 1 to 4 carbon atoms, or from 1 to 3 carbon atoms. It will beappreciated that a branched alkyl has a minimum of three carbon atoms.An alkyl group can be C₁₋₆ alkyl, C₁₋₄ alkyl, or C₁₋₃ alkyl. Examples ofalkyl groups include methyl, ethyl, n-propyl, iso-propyl, n-butyl,iso-butyl, tert-butyl, n-hexyl, n-decyl, and tetradecyl. An alkyl groupis C₁₋₆ alkyl, C₁₋₄ alkyl, and C₁₋₃ alkyl.

“Cycloalkanediyl” refers to a diradical saturated monocyclic orpolycyclic hydrocarbon group. A cycloalkanediyl group can be C₃₋₁₂cycloalkanediyl, C₃₋₈ cycloalkanediyl, C₃₋₆ cycloalkanediyl, or C₅₋₆cycloalkanediyl. Examples of cycloalkanediyl groups includecyclohexane-1,4-diyl, cyclohexane-1,3-diyl, and cyclohexane-1,2-diyl.

A “curable composition” refers to a composition that comprises at leasttwo reactants capable of reacting to form a cured composition. Forexample, a curable composition can comprise a thiol-terminatedpolythioether prepolymer and a polyepoxide capable of reacting to form acured polymer. A curable composition may include a catalyst for thecuring reaction and other components such as, for example, fillers,pigments, solvents, plasticizers, and adhesion promoters. A curablecomposition may be curable at ambient conditions such as roomtemperature and humidity, or may require exposure to elevatedtemperature, moisture, or other condition(s) to initiate and/or toaccelerate the curing reaction. A curable composition may initially beprovided as a two-part composition including a separate base componentand a separate accelerator component. The base composition can containone of the reactants participating in the curing reaction such as athiol-terminated polythioether prepolymer and the acceleratorcomposition can contain the other reactant such as a polyepoxide. Otheradditives can be included in the base and/or accelerator compositions.The two compositions can be mixed shortly before use to provide acurable composition. A curable composition can exhibit a viscositysuitable for a particular method of application. For example, a Class Asealant composition, which is suitable for brush-on applications, can becharacterized by a viscosity from 1 poise to 500 poise. A Class Bsealant composition, which is suitable for fillet seal applications, canbe characterized by a viscosity from 4,500 poise to 20,000 poise. AClass C sealant composition, which is suitable for fay sealapplications, can be characterized by a viscosity from 500 poise to4,500 poise. After the two components of a sealant system are combinedand mixed, the curing reaction can proceed and the viscosity of thecurable composition can increase and at some point will no longer beworkable. The duration between the time the two components are mixed toform the curable composition and the time the curable composition can nolonger be reasonably or practically applied to a surface for itsintended purpose and method of application can be referred to as theworking time. As can be appreciated, the working time can depend on anumber of factors including, for example, the curing chemistry, theapplication method, and the temperature. Once a curable composition isapplied to a surface (and during application), the curing reaction canproceed to provide a cured composition. A cured composition develops atack-free surfaces and fully cures over a period of time. A curablecomposition can be considered to be cured when the surface is tack-free,or can be considered cured, for example, when the Shore A hardness ofthe surface is 25A for a Class C sealant and 30A for a Class B sealant.

As used herein, “polymer” refers to oligomers, homopolymers, andcopolymers, which may be cured or uncured. Unless stated otherwise,molecular weights are number average molecular weights for polymericmaterials indicated as “M_(n)” as determined, for example, by gelpermeation chromatography using a polystyrene standard in anart-recognized manner. Unless stated otherwise, molecular weights arenumber average molecular weights for polymeric materials indicated as“Mn” as may be determined, for example, by end group analysis usingiodine titration.

“Prepolymers” refer to polymers prior to curing. In general, prepolymersprovided by the present disclosure are liquid at room temperature.“Adducts” refer to prepolymers that are functionalized with a reactiveterminal group; however, prepolymers may also contain terminalfunctional groups. Thus, the terms prepolymer and adduct are usedinterchangeably. The term adduct is often used to refer to a prepolymerthat is an intermediate in a reaction sequence used to prepare aprepolymer.

Specific gravity refers to the ratio of the density of a substance tothe density of water at room temperature and pressure. Specific gravitycan be measured according to ASTM D1475. The specific gravity of lowdensity filler such as microcapsules was measured according to ASTMD1475. The specific gravity of the composition and sealants wasdetermined according to ASTM D1473 modified to weigh the sealant inhexane.

Reference is now made to certain embodiments of compositions andmethods. The disclosed embodiments are not intended to be limiting ofthe claims. To the contrary, the claims are intended to cover allalternatives, modifications, and equivalents.

Compositions provided by the present disclosure can comprise athiol-terminated polythioether prepolymer, a polyepoxide, and lowdensity microcapsules. A composition can be formulated as a sealant,such as an aerospace sealant.

Compositions and sealant formulations provided by the present disclosurecan comprise a thiol-terminated polythioether prepolymer or combinationof thiol-terminated polythioether prepolymers.

Examples of suitable thiol-terminated polythioether prepolymers aredisclosed in U.S. Pat. No. 6,172,179, which is incorporated by referencein its entirety.

A thiol-terminated polythioether prepolymer can comprise athiol-terminated polythioether prepolymer comprising the chemicalstructure of Formula (1):

$\begin{matrix}{{–R}^{1}{–\left\lbrack {{{–S–}\left( {CH}_{2} \right)}_{2}{{–O–}\left\lbrack {{–R}^{2}{–O–}} \right\rbrack}_{m}{–\left( {CH}_{2} \right)}_{2}{–S–R}^{1}} \right\rbrack}_{n}–} & (1)\end{matrix}$

wherein,

-   -   each R¹ can independently comprise a C₂₋₁₀ n-alkanediyl group, a        C₃₋₆ branched alkanediyl group, a C₆₋₈ cycloalkanediyl group, a        C₆₋₁₀ alkanecycloalkanediyl group, a heterocyclic group, or a        —[(—CHR³—)_(p)—X—]_(q)—(CHR³)_(r)— group, wherein each R³ can        comprise from hydrogen or methyl;    -   each R² can independently comprise a C₂₋₁₀ n-alkanediyl group, a        C₃₋₆ branched alkanediyl group, a C₆₋₈ cycloalkanediyl group, a        C₆₋₁₄ alkanecycloalkanediyl group, a heterocyclic group, or a        —[(—CH₂-)_(p)—X—]_(q)—(CH₂)_(r)— group;    -   each X can independently comprise —O—, —S—, and —NR—, wherein R        can comprise from hydrogen or methyl;    -   m ranges from 0 to 50;    -   n is an integer ranging from 1 to 60;    -   p is an integer ranging from 2 to 6;    -   q is an integer ranging from 1 to 5; and r is an integer ranging        from 2 to 10.

In prepolymers of Formula (1), R¹ can be—[—(CHR³)_(p)—X-]_(q)—(CHR³)_(r)— wherein each X can independentlycomprise from —O— and —S—. In prepolymers of Formula (1), R¹ can be—[—(CHR³)_(p)—X-]_(q)—(CHR³)_(r)— each X can be —O— or each X can be—S—.

In prepolymers of Formula (1), R¹ can be —[—(CH₂)_(p)—X-]_(q)—(CH₂)_(r)—wherein each X can independently comprise from —O— and —S—. Inprepolymers of Formula (1), R¹ can be —[—(CH₂)_(p)—X-]_(q)—(CH₂)_(r)-?each X can be —O— or each X can be —S—.

In prepolymers of Formula (1), R¹ can be—[(—CH₂—)_(p)—X—]_(q)—(CH₂)_(r)—, where p can be 2, X can be O, q can be2, r can be 2, R² can be ethanediyl, m can be 2, and n can be 9.

In prepolymers of Formula (1), each R¹ can be derived fromdimercaptodioxaoctane (DMDO) or each R¹ can be derived fromdimercaptodiethylsulfide (DMDS).

In prepolymers of Formula (1), each m can be independently an integerfrom 1 to 3. Each m can be the same and can be 1, 2, or 3.

In prepolymers of Formula (1), n can be an integer from 1 to 30, aninteger from 1 to 20, an integer from 1 to 10, or an integer from 1 to5. In addition, n may be any integer from 1 to 60.

In prepolymers of Formula (1), each p can independently comprise 2, 3,4, 5, or 6. Each p can be the same and is 2, 3, 4, 5, or 6.

A thiol-terminated polythioether prepolymer can comprise Permapol®P3.1e, available from PRC-DeSoto International Inc.

A thiol-terminated polythioether prepolymer can comprise athiol-terminated polythioether prepolymer of Formula (2a), athiol-terminated polythioether prepolymer of Formula (2b), or acombination thereof:

$\begin{matrix}{\mspace{79mu}{{{HS}{–R}}^{1}{–\left\lbrack {{{–S–}\left( {CH}_{2} \right)}_{2}{{–O–}\left( {R^{2}{–O}} \right)}_{m}{–\left( {CH}_{2} \right)}_{2}{–S–R}^{1}–} \right\rbrack}_{n}{–SH}}} & \left( {2a} \right) \\{\left\{ {{{HS}{–R}}^{1}{–\left\lbrack {{{–S–}\left( {CH}_{2} \right)}_{2}{{–O–}\left( {R^{2}{–O}} \right)}_{m}{–\left( {CH}_{2} \right)}_{2}{–S–R}^{1}–} \right\rbrack}_{n}{–S–V}^{\prime}–} \right\}_{z}B} & \left( {2b} \right)\end{matrix}$

wherein,

-   -   each R¹ can independently comprise from C₂₋₁₀ alkanediyl, C₆₋₈        cycloalkanediyl, C₆₋₁₄ alkanecycloalkanediyl, C₅₋₈        heterocycloalkanediyl, or —[(—CHR³—)_(p)—X—]_(q)—(—CHR³—)_(r)—,        wherein,        -   p is an integer from 2 to 6;        -   q is an integer from 1 to 5;        -   r is an integer from 2 to 10;        -   each R³ can independently comprise hydrogen or methyl; and        -   each X can independently comprise —O—, —S—, or —NR—, wherein            R can comprise hydrogen or methyl;    -   each R² can independently comprise C₁₋₁₀ alkanediyl, C₆₋₈        cycloalkanediyl, C₆₋₁₄ alkanecycloalkanediyl, or        —[(—CHR³—)_(p)—X—]_(q)—(—CHR³—)_(r)—, wherein p, q, r, R³, and X        are as defined as for R¹;    -   m is an integer from 0 to 50;    -   n is an integer from 1 to 60;    -   B represents a core of a z-valent, polyfunctionalizing agent        B(—V)_(z) wherein,        -   z is an integer from 3 to 6; and        -   each V is a moiety comprising a terminal group reactive with            a thiol; and    -   each —V′— is derived from the reaction of —V with a thiol.

In prepolymers of Formula (2a) and Formula (2b), R¹ can be—[(—CH₂-)_(p)—X—]_(q)—(CH₂)_(r)—, where p can be 2, X can be —O—, q canbe 2, r can be 2, R² can be ethanediyl, m can be 2, and n can be 9.

In prepolymers of Formula (2a) and Formula (2b), R¹ can comprise C₂₋₆alkanediyl or —[—(CHR³)_(p)—X-]_(q)—(CHR³)_(r)—.

In prepolymers of Formula (2a) and Formula (2b), R¹ can comprise—[—(CHR³)_(p)—X-]_(q)—(CHR³)_(r)—, X can be —O— or X can be —S—.

In prepolymers of Formula (2a) and Formula (2b), where R¹ can comprise—[—(CHR³)_(p)—X-]_(q)—(CHR³)_(r)—, p can be 2, r can be 2, q can be 1,and X can be —S—; or wherein p can be 2, q can be 2, r can be 2, and Xcan be —O—; or p can be 2, r can be 2, q can be 1, and X can be —O—.

In prepolymers of Formula (2a) and Formula (2b), where R¹ can comprise—[—(CHR³)_(p)—X-]_(q)—(CHR³)_(r)—, each R³ can comprise hydrogen, or atleast one R³ can comprise methyl.

In prepolymers of Formula (2a) and Formula (2b), each R¹ can be thesame, or at least one R¹ can be different.

Various methods can be used to prepare thiol-terminated polythioetherprepolymers of Formula (2a) and Formula (2b). Such thiol-terminatedpolythioether prepolymers may be difunctional, that is, linear polymershaving two terminal thiol groups, or polyfunctional, that is, branchedpolymers have three or more terminal thiol groups. Suitablethiol-terminated polythioether prepolymers are commercially available,for example, as Permapol® P3.1e, from PRC-DeSoto International Inc.

A thiol-terminated polythioether prepolymer can be a combination ofPermapol® P3.1e prepolymers having different thiol functionalities.

A thiol-terminated polythioether prepolymer may comprise a mixture ofdifferent thiol-terminated polythioethers and the thiol-terminatedpolythioethers may have the same or different functionality. Athiol-terminated polythioether prepolymer has an average functionalityfrom 2 to 6, from 2 to 4, from 2 to 3, from 2.05 to 2.8, or from 2.05 to2.5. For example, a thiol-terminated polythioether prepolymer cancomprise a difunctional thiol-terminated polythioether, a trifunctionalthiol-terminated polythioether or a combination thereof.

A thiol-terminated polythioether prepolymer can be prepared by reactinga polythiol and a diene such as a divinyl ether, and the respectiveamounts of the reactants used to prepare the polythioethers are chosento yield terminal thiol groups. Thus, in some cases, (n or >n, such asn+1) moles of a polythiol, such as a dithiol or a mixture of at leasttwo different dithiols and about 0.05 moles to 1 moles, such as 0.1moles to 0.8 moles, of a thiol-terminated polyfunctionalizing agent maybe reacted with (n) moles of a diene, such as a divinyl ether, or amixture of at least two different dienes, such as a divinyl ether. Athiol-terminated polyfunctionalizing agent is present in the reactionmixture in an amount sufficient to provide a thiol-terminatedpolythioether having an average functionality of from 2.05 to 3, such asfrom 2.1 to 2.8, or from 2.1 to 2.6.

The reaction used to make a thiol-terminated polythioether prepolymermay be catalyzed by a free radical catalyst. Suitable free radicalcatalysts include azo compounds, for example azobisnitrile compoundssuch as azo(bis)isobutyronitrile (AIBN); organic peroxides, such asbenzoyl peroxide and t-butyl peroxide; and inorganic peroxides, such ashydrogen peroxide. The reaction can also be effected by irradiation withultraviolet light either with or without a radicalinitiator/photosensitizer. Ionic catalysis methods, using eitherinorganic or organic bases, e.g., triethylamine, may also be used.

Suitable thiol-terminated polythioether prepolymers may be produced byreacting a divinyl ether or mixtures of divinyl ethers with an excess ofdithiol or a mixtures of dithiols.

Thus, a thiol-terminated polythioether prepolymer can comprise thereaction product of reactants comprising:

(a) a dithiol of Formula (3):

HS—R¹—SH  (3)

-   -   wherein,        -   R¹ can comprise C₂₋₆ alkanediyl, O, x cycloalkanediyl, C₆₋₁₀            alkanecycloalkanediyl, C₅₋₈ heterocycloalkanediyl, or            —[—(CHR³)_(p)—X-]_(q)—(CHR³)_(r)—; wherein,            -   each R³ can independently comprise hydrogen or methyl;            -   each X can independently comprise —O—, —S—, —NH—, or                —N(—CH₃)—;            -   p is an integer from 2 to 6;            -   q is an integer from 1 to 5; and            -   r is an integer from 2 to 10; and

(b) a divinyl ether of Formula (4):

$\begin{matrix}{{CH}_{2}\text{=}{{{CH}{–O–}}\left\lbrack {{–R}^{2}{–O–}} \right\rbrack}_{m}{–CH}\text{=}{CH}_{2}} & (4)\end{matrix}$

-   -   wherein,        -   each R² can independently comprise C₁₋₁₀ alkanediyl, C₆₋₈            cycloalkanediyl, C₆₋₁₄ alkanecycloalkanediyl, or            —[(—CHR³—)_(p)—X—]_(q)—(—CHR³—)_(r)—, wherein p, q, r, R³,            and X are as defined above; and        -   m is an integer from 0 to 50.

The reactants may further comprise (c) a polyfunctional compound such asa polyfunctional compound B(—V)_(z), where B, —V, and z are as definedherein.

Dithiols suitable for use in preparing thiol-terminated polythioetherprepolymers include those having the structure of Formula (3):

$\begin{matrix}{{{HS}{–R}}^{1}{–SH}} & (3)\end{matrix}$

wherein,

-   -   R¹ can comprise C₂₋₆ alkanediyl, C₆₋₈ cycloalkanediyl, C₆₋₁₀        alkanecycloalkanediyl, C₅₋₈ heterocycloalkanediyl, or        —[—(CHR³)_(p)—X-]_(q)—(CHR³)_(r)—; wherein,        -   each R³ can independently comprise hydrogen or methyl;        -   each X can independently comprise —O—, —S—, or —NR— wherein            R can comprise hydrogen or methyl;        -   p is an integer from 2 to 6;        -   q is an integer from 1 to 5; and        -   r is an integer from 2 to 10.

In dithiols of Formula (3), R¹ is —[—(CHR³)_(p)—X-]_(q)—(CHR³)_(r)—.

In dithiols of Formula (3), X can comprise —O— or —S—, and thus—[—(CHR³)_(p)—X-]_(q)—(CHR³)_(r)— in Formula (3) can be—[(—CHR³—)_(p)—O—]_(q)—(CHR³)_(r)— or —[(—CHR³₂-)_(p)—S—]_(q)—(CHR³)_(r)—. P and r can be equal, such as where p and rcan be both two.

In dithiols of Formula (3), R¹ can comprise C₂₋₆ alkanediyl and—[—(CHR³)_(p)—X-]_(q)—(CHR³)_(r)—.

In dithiols of Formula (3), R¹ can comprise—[—(CHR³)_(p)—X-]_(q)—(CHR³)_(r)—, and X can be —O—, or X can be —S—.

In dithiols of Formula (3) where R¹ can comprise—[—(CHR³)_(p)—X-]_(q)—(CHR³)_(r)—, p can be 2, r can be 2, q can be 1,and X can be —S—; or p can be 2, q can be 2, r can be 2, and X can be—O—; or p can be 2, r can be 2, q can be 1, and X can be —O—.

In dithiols of Formula (3) where R¹ can comprise—[—(CHR³)_(p)—X-]_(q)—(CHR³)_(r)—, each R³ can be hydrogen, or at leastone R³ can be methyl.

In dithiols of Formula (3), each R¹ can comprise derived fromdimercaptodioxaoctane (DMDO) or each R¹ can be derived fromdimercaptodiethylsulfide (DMDS).

In dithiols of Formula (3), each m can be independently an integer from1 to 3. Each m can be the same and is 1,2, or 3.

In dithiols of Formula (3), n can be an integer from 1 to 30, an integerfrom 1 to 20, an integer from 1 to 10, o an integer from 1 to 5. N maybe any integer from 1 to 60.

In dithiols of Formula (3), each p can independently comprise 2, 3, 4,5, and 6. Each p can be the same and can be 2, 3, 4, 5, or 6.

Examples of suitable dithiols include 1,2-ethanedithiol,1,2-propanedithiol, 1,3-propanedithiol, 1,3-butanedithiol,1,4-butanedithiol, 2,3-butanedithiol, 1,3-pentanedithiol,1,5-pentanedithiol, 1,6-hexanedithiol, 1,3-dimercapto-3-methylbutane,dipentenedimercaptan, ethylcyclohexyldithiol (ECHDT),dimercaptodiethylsulfide, methyl-substituted dimercaptodiethylsulfide,dimethyl-substituted dimercaptodiethylsulfide, dimercaptodioxaoctane,1,5-dimercapto-3-oxapentane, and a combination of any of the foregoing.

A dithiol may have one or more pendent groups comprising a lower (e.g.,C₁₋₆) alkyl group, a lower alkoxy group, or a hydroxy group. Suitablealkyl pendent groups include, for example, C₁₋₆ linear alkyl, C₃₋₆branched alkyl, cyclopentyl, and cyclohexyl.

Other examples of suitable dithiols include dimercaptodiethylsulfide(DMDS) (in Formula (3), R¹ is —[(—CH₂-)_(p)—X—]_(q)—(CH₂)_(r)—, whereinp is 2, r is 2, q is 1, and X is —S—); dimercaptodioxaoctane (DMDO) (inFormula (3), R¹ is —[(—CH₂-)_(p)—X—]_(q)—(CH₂)_(r)—, wherein p is 2, qis 2, r is 2, and X is —O—); and 1,5-dimercapto-3-oxapentane (in Formula(3), R¹ is —[(—CH₂-)_(p)—X—]_(q)—(CH₂)_(r)—, wherein p is 2, r is 2, qis 1, and X is —O—). It is also possible to use dithiols that includeboth heteroatoms in the carbon backbone and pendent alkyl groups, suchas methyl groups. Such compounds include, for example,methyl-substituted DMDS, such as HS—CH₂CH(CH₃)—S—CH₂CH₂—SH,HS—CH(CH₃)CH₂—S—CH₂CH₂—SH and dimethyl substituted DMDS, such asHS—CH₂CH(CH₃)—S—CHCH₃CH₂—SH and HS—CH(CH₃)CH₂—S—CH₂CH(CH₃)—SH.

Suitable divinyl ethers for preparing thiol-terminated polythioethersinclude, for example, divinyl ethers of Formula (4):

$\begin{matrix}{{CH}_{2}\text{=}{{{CH}{–O–}}\left\lbrack {{–R}^{2}{–O–}} \right\rbrack}_{m}{–CH}\text{=}{CH}_{2}} & (4)\end{matrix}$

where R² in Formula (4) can comprise a C₂₋₆ n-alkanediyl group, a C₃₋₆branched alkanediyl group, a C₆₋₈ cycloalkanediyl group, a C₆₋₁₀alkanecycloalkanediyl group, and —[(—CH₂-)_(p)—O—]_(q)—(—CH₂—)_(r)—,where p can be an integer ranging from 2 to 6, q can be an integer from1 to 5, and r can be an integer from 2 to 10. In a divinyl ether ofFormula (4), R² can be a C₂₋₆ n-alkanediyl group, a C₃ 6 branchedalkanediyl group, a C₆₋₈ cycloalkanediyl group, a C₆₋₁₀alkanecycloalkanediyl group, or —[(—CH₂-)_(p)—O—]_(q)—(—CH₂—)_(r)—.

Suitable divinyl ethers include, for example, compounds having at leastone oxyalkanediyl group, such as from 1 to 4 oxyalkanediyl groups, i.e.,compounds in which m in Formula (4) can be an integer ranging from 1 to4. In divinyl ethers of Formula (4) m can be an integer ranging from 2to 4. It is also possible to employ commercially available divinyl ethermixtures that are characterized by a non-integral average value for thenumber of oxyalkanediyl units per molecule. Thus, m in Formula (4) canalso take on rational number values ranging from 0 to 10.0, such as from1.0 to 10.0, from 1.0 to 4.0, or from 2.0 to 4.0.

Examples of suitable vinyl ethers include, divinyl ether, ethyleneglycol divinyl ether (EG-DVE) (R² in Formula (4) can be ethanediyl and mis 1), butanediol divinyl ether (BD-DVE) (R² in Formula (4) can bebutanediyl and m is 1), hexanediol divinyl ether (F1D-DVE) (R² inFormula (4) can be hexanediyl and m is 1), diethylene glycol divinylether (DEG-DVE) (R² in Formula (4) can be ethanediyl and m is 2),triethylene glycol divinyl ether (R² in Formula (4) can be ethanediyland m is 3), tetraethylene glycol divinyl ether (R² in Formula (4) canbe ethanediyl and m is 4), cyclohexanedimethanol divinyl ether,polytetrahydrofuryl divinyl ether; trivinyl ether monomers, such astrimethylolpropane trivinyl ether; tetrafunctional ether monomers, suchas pentaerythritol tetravinyl ether; and combinations of two or moresuch polyvinyl ether monomers. A polyvinyl ether may have one or morependent groups comprising alkyl groups, hydroxy groups, alkoxy groups,or amine groups.

Divinyl ethers in which R² in Formula (4) is C₃₋₆ branched alkanediylmay be prepared by reacting a polyhydroxy compound with acetylene.Examples of divinyl ethers of this type include compounds in which R² inFormula (4) is an alkyl-substituted methanediyl group such as—CH(—CH₃)—, for which R² in Formula (4) is ethanediyl and m is 3 or analkyl-substituted ethanediyl.

Other useful divinyl ethers include compounds in which R² in Formula (4)is polytetrahydrofuryl (poly-THF) or polyoxyalkanediyl, such as thosehaving an average of about 3 monomer units.

Two or more types of polyvinyl ether monomers of Formula (4) may beused. Thus, two dithiols of Formula (3) and one polyvinyl ether monomerof Formula (4), one dithiol of Formula (3) and two polyvinyl ethermonomers of Formula (4), two dithiols of Formula (3) and two divinylether monomers of Formula (4), and more than two compounds of one orboth Formula (3) and Formula (4), may be used to produce a variety ofthiol-terminated polythioethers.

A polyvinyl ether monomer can comprise 20 mole percent to less than 50mole percent of the reactants used to prepare a thiol-terminatedpolythioether, or 30 mole percent to less than 50 mole percent.

Relative amounts of dithiols and divinyl ethers can be selected to yieldpolythioethers having terminal thiol groups. Thus, a dithiol of Formula(3) or a mixture of at least two different dithiols of Formula (3), canbe reacted with of a divinyl ether of Formula (4) or a mixture of atleast two different divinyl ethers of Formula (4) in relative amountssuch that the molar ratio of thiol groups to alkenyl groups is greaterthan 1:1, such as from 1.1 to 2.0:1.0.

The reaction between dithiols and divinyl ethers and/or polythiols andpolyvinyl ethers may be catalyzed by a free radical catalyst. Suitablefree radical catalysts include, for example, azo compounds, for exampleazobisnitriles such as azo(bis)isobutyronitrile (AIBN); organicperoxides such as benzoyl peroxide and t-butyl peroxide; and inorganicperoxides such as hydrogen peroxide. The catalyst may be a free-radicalcatalyst, an ionic catalyst, or ultraviolet radiation. In certainreactions, the catalyst does not comprise acidic or basic compounds, anddoes not produce acidic or basic compounds upon decomposition. Examplesof suitable free-radical catalysts include azo-type catalysts, such asVAZO®-57 (Du Pont), VAZO®-64 (Du Pont), VAZO®-67 (Du Pont), V-70® (WakoSpecialty Chemicals), and V-65B® (Wako Specialty Chemicals). Examples ofother free-radical catalysts include alkyl peroxides, such as t-butylperoxide. The reaction may also be effected by irradiation withultraviolet light either with or without a cationic photoinitiatingmoiety.

Thiol-terminated polythioether prepolymers provided by the presentdisclosure may be prepared by combining at least one dithiol of Formula(3) and at least one divinyl ether of Formula (4) followed by additionof an appropriate catalyst, and carrying out the reaction at atemperature from 30° C. to 120° C., such as 70° C. to 90° C., for a timefrom 2 hours to 24 hours, such as 2 hours to 6 hours.

Thiol-terminated polythioether prepolymers may comprise a polyfunctionalpolythioether prepolymer, i.e., may have an average functionality ofgreater than 2.0. Suitable polyfunctional thiol-terminatedpolythioethers include, for example, those having the structure ofFormula (2b):

$\begin{matrix}{\left\{ {{{HS}{–R}}^{1}{–\left\lbrack {{{–S–}\left( {CH}_{2} \right)}_{2}{{–O–}\left( {R^{2}{–O}} \right)}_{m}{–\left( {CH}_{2} \right)}_{2}{–S–R}^{1}–} \right\rbrack}_{n}{–S–V}^{\prime}–} \right\}_{z}B} & \left( {2b} \right)\end{matrix}$

where z has an average value of greater than 2.0, and, a value between 2and 3, a value between 2 and 4, a value between 3 and 6, or can be aninteger from 3 to 6.

Polyfunctionalizing agents suitable for use in preparing suchpolyfunctional thiol-terminated polymers include trifunctionalizingagents, that is, compounds where z is 3. Suitable trifunctionalizingagents include, for example, triallyl cyanurate (TAC),1,2,3-propanetrithiol, isocyanurate-containing trithiols, andcombinations thereof, as disclosed in U.S. Application Publication No.2010/0010133, which is incorporated by reference in its entirety, andisocyanurates as disclosed, for example, in U.S. Application PublicationNo. 2011/0319559, which is incorporated by reference in its entirety.Other useful polyfunctionalizing agents include trimethylolpropanetrivinyl ether, and the polythiols described in U.S. Pat. Nos.4,366,307; 4,609,762; and 5,225,472, each of which is incorporated byreference in its entirety. Mixtures of polyfunctionalizing agents mayalso be used. As a result, polythioethers provided by the presentdisclosure may have a wide range of average functionality. For example,trifunctionalizing agents may afford average functionalities from 2.05to 3.0, such as from 2.1 to 2.6. Wider ranges of average functionalitymay be achieved by using tetrafunctional or higher functionalitypolyfunctionalizing agents. Functionality may also be determined byfactors such as stoichiometry, as will be understood by those skilled inthe art.

In thiol-terminated polythioether prepolymers of Formula (2a) andFormula (2b) the prepolymers can be the reaction product of DMDO,diethylene glycol divinyl ether, and triallyl cyanurate (TAC), whereinR¹ is —[(—CH₂-)_(p)—X—]_(q)—(CH₂)_(r)—, wherein p is 2, q is 2, r is 2,and X is —O—; R² is —(CH₂)₂— and m is 2; and B(—V)_(z) has the structureof Formula (5):

A thiol-terminated polythioether prepolymer can be a combination ofthiol-terminated polythioethers having different thiol functionalities.For example, a thiol terminated polythioether can be a combination ofthiol-terminated polythioethers having a functionality of 2.2 and afunctionality of 2.8. A thiol-terminated polythioether can comprise from95 wt % to 99.5 wt % of a thiol-terminated polythioether having a thiolfunctionality of 2.2 and from 0.5 wt % to 5 wt % of a thiol-terminatedpolythioether having a functionality of 2.8, where wt % is based on thetotal weight of the thiol-terminated polythioether.

Compositions and sealants provided by the present disclosure cancomprise a curing agent, i.e., crosslinking agent, comprising a compoundreactive with thiol groups. Examples of suitable curing agents includepolyepoxides, Michael acceptors, and polyalkenyls. Suitable curingagents can comprise two or more groups reactive with thiol groups.

Compositions and sealants provided by the present disclosure cancomprise a polyepoxide curing agent or a combination of poly epoxidecuring agents. A poly epoxide refers to a compound having two or morereactive epoxy groups. A polyepoxide can be difunctional or can includea combination of polyepoxides having different epoxy functionalities. Apolyepoxide may include a combination of polyepoxides. A polyepoxideresin can be liquid at room temperature.

Examples of suitable polyepoxide curing agents include hydantoindiepoxide, a diglycidyl ether of bisphenol-A, a diglycidyl ether ofbisphenol-F, a novolac-type polyepoxide, epoxidized unsaturated phenolicresins, dimer acid-based epoxy resins, and combinations of any of theforegoing.

Sealant compositions provided by the present disclosure can include astoichiometric excess of the curing agent compared to thethiol-terminated polythioether. For example, a sealant composition maycontain from 1.1 to 1.3 epoxy equivalents to 1 thiol equivalent or from1.15 to 1.25 epoxy equivalents to 1 thiol equivalent.

Other examples of suitable polyepoxides include a bisphenol A typepolyepoxide, a brominated bisphenol A type polyepoxide, a bisphenol Ftype polyepoxide, a biphenyl type polyepoxide, a novolac typepolyepoxide, an alicyclic polyepoxide, a naphthalene type polyepoxide,an ether or polyether polyepoxide, an oxirane ring-containingpolybutadiene, and a silicone polyepoxy copolymer.

Additional examples of suitable poly epoxides include a bisphenol A typepoly epoxide having an average molecular weight, for example of 400Daltons or less 600 Daltons or less, 1,000 Daltons or less, 1,200Daltons or less, or 1,400 Daltons or less; a branched polyfunctionalbisphenol A type polyepoxide such as p-glycidyloxyphenyldimethyltolylbisphenol A diglycidyl ether: a bisphenol F type epoxyresin; a phenol novolac type polyepoxide having an average molecularweight, for example, of 500 Daltons or less, 700 Daltons or less, 1,000Daltons or less, or 1,500 Daltons or less; an alicyclic polyepoxide suchas vinyl(3,4-cyclohexene)dioxide, methyl 3,4-epoxycyclohexylcarboxylate(3,4-epoxycyclohexyl), bis(3,4-epoxy-6-methylcyclohexylmethyl) adipateand 2-(3,4-epoxycyclohexyl)-5,1-spiro(3,4-epoxycyclohexyl)-m-dioxane; abiphenyl type polyepoxide such as3,3′,5,5′-tetramethyl-4,4′-diglycidyloxybiphenyl; a glycidyl ester typepolyepoxide such as diglycidyl hexahydrophthalate, diglycidyl3-methylhexahydrophthalate and diglycidyl hexahydroterephthalate; aglycidyl amine type polyepoxide such as diglycidylaniline,diglycidyltoluidine, triglycidyl-p-aminophenol, tetraglycidyl-m-xylenediamine, tetraglycidylbis(aminomethyl)cyclohexane; a hydantoin typepolyepoxide such as 1,3-diglycidyl-5-methyl-5-ethylhydantoin; and anaphthalene ring-containing polyepoxide. Also, a polyepoxide havingsilicone such as1,3-bis(3-glycidoxy-propyl)-1,1,3,3-tetramethyldisiloxane may be used.

Examples of commercially available polyepoxides suitable for use incompositions and sealants provided by the present disclosure includepolyglycidyl derivatives of phenolic compounds, such as those availableunder the trade names EPON™ 824, EPON™ 825, EPON™ 826, EPON™ 827, EPON™828, EPON™ 829, EPON™ 830, EPON™ 834, EPON™ 862, EPON™ 863, EPON™ 8280,EPON™ 8281, EPON™ 872, an EPON™ resin blend, EPON™ 1001-A-80, EPON™1001-B-80, EPON™ 1001-CX-75, EPON™ 1001-DNT-75, EPON™ 1001-FT-75, EPON™1001-G-70, EPON™1001-H-75, EPON™ 1001-K-65, EPON™ 1001-O-75, EPON™1001-T-75, EPON™ 1001-UV-70, EPON™ 1001-X-75, EPON™ 1004-O-65, EPON™1007-CT-55, EPON™ 1007-FMXJ-50, EPON™1007-HT-55, EPON™ 1009-DU-40, EPON™1009-MX-40, and other EPON™ epoxy resins, available, for example, fromMomentive Specialty Chemicals Inc. and/or from Resolution PerformanceProducts LLC; and DER™ 331, DER™ 332, DER™ 334, DER™ 354, DER™ 383 andDER™ 542 from Dow Chemical Co. Other suitable polyepoxides includepolyepoxides prepared from polyols and polyglycidyl derivatives ofphenol-formaldehyde novolacs, the latter of which are commerciallyavailable under the trade names DEN™ 431, DEN™ 438, and DEN™ 439 fromDow Chemical Company. Cresol analogs are also available commerciallyECN™ 1235, ECN™ 1273, and ECN™ 1299 from Ciba Specialty Chemicals, Inc.SU-8 is a bisphenol A-type epoxy Novolae available from. ResolutionPerformance Products EEC. Polygiyeidyl adducts of amines, aminoalcoholsand polycarboxylic acids are also useful in this invention, commerciallyavailable resins of which include GLYAMINE™ 135, GLYAMINE™ 125, and GLYAMINE™ 115; ARALDITE™ MY-720, ARALDITE™ MY-721, ARALDITE™ 0500, andARALDITE™ 0510 from Ciba Specialty Chemicals, Inc. and PGA-X and PGA-C.

Compositions can comprise, for example, from 10 wt % to 30 wt % of apoly epoxide, from 12 wt % to 28 wt %, from 14 wt % to 26 wt %, from 16wt % to 24 wt %, or from 18 wt % to 22 wt % of a polyepoxide, wherein wt% is based on the total weight of the composition.

A polyepoxide can include a combination of polyepoxides.

A polyepoxide can comprise, for example, at least 85 wt % of adiglycidyl ether of bisphenol A, such as at least 90 wt %, or at least95 wt %, wherein wt % is based on the total weight of the polyepoxide ina composition.

A polyepoxide can comprise, for example, from 85 wt % to 99 wt % of adiglycidyl ether of bisphenol A, from 87 wt % to 97 wt %, from 89 wt %to 95 wt %, or from 91 wt % to 93 wt %, where wt % is based on the totalweight of the polyepoxide in a composition.

A polyepoxide can comprise, for example, from 1 wt % to 11 wt % of anovolac polyepoxide, from 2 wt % to 9 wt %, or from 4 wt % to 7 wt % ofa novolac poly epoxide, where wt % is based on the total weight of thepolyepoxide in a composition.

A polyepoxide can comprise, for example, from 86 wt % to 99 wt % of adiglycidyl ether of bisphenol A and from 1 wt % to 11 wt % of a novolacpoly epoxide; from 88 wt % to 97 wt % of a diglycidyl ether of bisphenolA and from 3 wt % to 9 wt % of a novolac polyepoxide; or from 90 wt % to95 wt % of a diglycidyl ether of bisphenol A and from 5 wt % to 7 wt %of a novolac polyepoxide; wherein wt % is based on the total weight ofthe polyepoxide in a composition.

A polyepoxide can comprise a hydroxyl-functional polyepoxide orcombination of hydroxyl-functional polyepoxides. For example, apolyepoxide can comprise a hydroxyl-functional diglycidyl ether ofbisphenol A.

A diglycidyl ether of bisphenol A can comprise pendent hydroxyl groupssuch as, for example, from 1 to 10 pendent hydroxyl groups, from 1 to 8hydroxyl groups, from 1 to 6 hydroxyl groups, from 1 to 4 pendenthydroxyl groups, or from 1 to 2 pendent hydroxyl groups, such as 1, 2,3, 4 5, or 6 pendent hydroxyl groups. A diglycidyl ether of bisphenol Ahaving pendent hydroxyl groups can be referred to as hydroxyl-functionaldiglycidyl ether of bisphenol A.

Hydroxyl-functional diglycidyl ethers of bisphenol A can have an epoxyequivalent weight from 400 Daltons to 1,500 Daltons, from 400 Daltons to1,000 Daltons or from 400 Daltons to 600 Daltons.

A diglycidyl ether of bisphenol A can comprise a diglycidyl ether ofbisphenol A without a hydroxyl-functional component, a diglycidyl etherof bisphenol A which ci partly hydroxyl-functional, or all of thediglycidyl ether of bisphenol A can be hydroxyl-functional.

A diglycidyl ether of bisphenol A having hydroxyl pendent groups canhave the structure:

where n is an integer from 1 to 6, or n is within a range from 1 to 6.

Examples of suitable diglycidyl ethers of bisphenol A include bisphenolA polyepoxides in which n is an integer from 1 to 6, or a combination ofbisphenol A polyepoxides in which n can be a non-integer value, forexample, from 0.1 to 2.9, from 0.1 to 2.5, from 0.1 to 2.1, from 0.1 to1.7, from 0.1 to 1.5, from 0.1 to 1.3, from 0.1 to 1.1, from 0.1 to 0.9,from 0.3 to 0.8, or from 0.5 to 0.8.

A diglycidyl ether of bisphenol A comprising hydroxyl pendent groups cancomprise, for example, a 2,2-bis(p-glycidyloxyphenyl)propanecondensation product with 2,2-bis(p-hydroxyphenyl)propane and similarisomers. Suitable diglycidyl ethers of bisphenol A comprising hydroxylpendent groups are available, for example, from Momentive and includeEPON™ solid epoxy resins such as EPON™ 100IF, EPON™ 1002F, EPON™ 1004F,EPON™ 1007F, EPON™ 1009F, and combinations of any of the foregoing. Suchdiglycidyl ethers of bisphenol A may be provided, for example, as a 70wt % to 95 wt % solids solution in a suitable solvent such as methylethyl ketone. Such high solids content resins include, for example,EPON™ 1001-A-80, EPON™ 1001-B-80, EPON™1001-CX-75, EPON™ 1001-DNT-75,EPON™ 1001-FT-75, EPON™ 1001-G-70, EPON™ 1001-H-75, EPON™ 1001-K-65,EPON™ 1001-O-75, EPON™ 1001-T-75, EPON™ 1001-UY-70, EPON™ 1001-X-75,EPON™ 1004-O-65, EPON™ 1007-CT-55, EPON™¹ 1007-FMU-50, EPON™ 1007-HT-55,EPON™ 1001-DU-40, EPON™ 1009-MX-840, or a combination of any of theforegoing.

Examples of suitable epoxy novolac resins include novolac polyepoxidesin which n is an integer from 1 to 6, from 1 to 4, or from 1 to 2; or inwhich n can be a non-integer value, for example, from 0.1 to 2.9, from0.1 to 2.5, from 0.1 to 2.1, from 0.1 to 1.7, from 0.1 to 1.5, from 0.1to 1.3, from 0.1 to 1.1, from 0.1 to 0.9, from 0.3 to 0.8, or from 0.5to 0.8.

A poly epoxide can comprise, for example, a difunctional poly epoxide, apoly epoxide having an epoxy functionality greater than 2 such as from 3to 6, or a combination thereof. A polyepoxide can have an average epoxyfunctionality, for example, from 2.1 to 3.5, from 2.2 to 3.4, from 2.6to 3.2, or from 2.7 to 3.1.

A poly epoxide can comprise, for example, a combination of adifunctional poly epoxide or combination of difunctional polyepoxides, atrifunctional polyepoxide or combination of trifunctional poly epoxides,or a combination of any of the foregoing.

Compositions provided by the present disclosure can comprise, forexample, from 86 wt % to 99 wt % of a difunctional polyepoxide and from1 wt % to 11 wt % of a trifunctional polyepoxide; from 88 wt % to 97 wt% of a difunctional polyepoxide and from 3 wt % to 9 wt % of atrifunctional polyepoxide; or from 90 wt % to 95 wt % of a difunctionalpolyepoxide and from 5 wt % to 7 wt % of a trifunctional polyepoxide;wherein wt % is based on the total weight of the polyepoxide in acomposition.

A difunctional poly epoxide can have an epoxy equivalent weight, forexample, from 400 Daltons to 1,500 Daltons, from 400 Daltons to 1,000Daltons, or from 400 Daltons to 600 Daltons.

A trifunctional poly epoxide can have an epoxy equivalent weight, forexample, from 140 Daltons to 500 Daltons, from 150 Daltons to 300Daltons, or from 160 Daltons to 200 Daltons.

A difunctional poly epoxide can comprise, for example, ahydroxyl-functional poly epoxide and a trifunctional polyepoxide cancomprise a hydroxyl-functional polyepoxide.

A composition can comprise, for example, a hydroxyl-functional polyepoxide and a trifunctional poly epoxide that does not contain pendenthydroxyl groups; or a composition can comprise a difunctionalpolyepoxide that does not contain pendent hydroxyl groups, and ahydroxyl-functional trifunctional polyepoxide.

Compositions provided by the present disclosure can comprise, forexample, from 86 wt % to 99 wt % of a hydroxyl-functional difunctionalpolyepoxide and from 1 wt % to 11 wt % of a trifunctional poly epoxide;from 88 wt % to 97 wt % of a hydroxyl-functional difunctional polyepoxide and from 3 wt % to 9 wt % of a trifunctional polyepoxide; orfrom 90 wt % to 95 wt % of a hydroxyl-functional difunctionalpolyepoxide and from 5 wt % to 7 wt % of a trifunctional polyepoxide;where wt % is based on the total weight of the polyepoxide in acomposition.

Compositions provided by the present disclosure can comprise, forexample, from 86 wt % to 99 wt % of a hydroxyl-functional polyepoxideand from 1 wt % to 11 wt % of a non-hydroxyl-functional poly epoxide;from 88 wt % to 97 wt % of a hydroxyl-functional poly epoxide and from 3wt % to 9 wt % of a non-hydroxyl-functional polyepoxide; or from 90 wt %to 95 wt % of a hydroxyl-functional polyepoxide and from 5 wt % to 7 wt% of a non-hydroxyl-functional polyepoxide; where wt % is based on thetotal weight of the polyepoxide in a composition.

A polyepoxide suitable for use in compositions provided by the presentdisclosure can comprise, for example, from 2 wt % to 10 wt % of a polyepoxide having an average epoxy functionality from 2.6 to 3.2, from 3 wt% to 9 wt %, from 4 wt % to 8 wt %, from 5 wt % to 7 wt %, or 6 wt % ofa polyepoxide having an average epoxy functionality from 2.6 to 3.0; andfrom 90 wt % to 98 wt % of a difunctional poly epoxide, from 91 wt % to97 wt %, from 92 wt % to 96 wt %, from 93 wt % to 95 wt %, or 94 wt % ofa difunctional polyepoxide, where wt % is based on the total weight ofthe polyepoxide in a composition.

A difunctional poly epoxide can comprise a hydroxyl-functional polyepoxide.

Compositions provided by the present disclosure can comprise acombination of polyepoxides. A combination of polyepoxides can comprisepolyepoxides having different polyepoxides having differentfunctionalities or different average functionalities. For example, acombination of polyepoxides can comprise a polyepoxide having an averageepoxy functionality from 2.7 to 2.9 such as 2.8 and a polyepoxide havingan epoxy functionality of 2. Polyepoxides having a higher averagefunctionality can increase the cross-linking density of a cured polymernetwork, which can lead to increased tensile strength, but also canreduce the % elongation of a cured sealant. Polyepoxides having a lowepoxy functionality such as around 2 can result in a cured compositionthat is more flexible. Because low density compositions have a highcontent of filler microcapsules, which tends to increase the tensilestrength of a cured sealant, it can be desirable to use polyepoxides orcombinations of polyepoxides having an epoxy functionality from 2 to 3,such as from 2 to 2.5, or from 2 to 2.3.

Compositions of the present disclosure can comprise at least oneinorganic filler in addition to low density microcapsules. An inorganicfiller can be included to provide mechanical reinforcement and tocontrol the rheological properties of the sealant composition.

Inorganic fillers may be added to compositions to impart desirablephysical properties such as, for example, to increase the impactstrength, to control the viscosity, or to modify the electricalproperties of a cured composition. Inorganic fillers useful incompositions provided by the present disclosure and useful for aviationand aerospace applications include carbon black, calcium carbonate,precipitated calcium carbonate, calcium hydroxide, hydrated alumina(aluminum hydroxide), fumed silica, silica, and combinations of any ofthe foregoing.

Inorganic filler can comprise a combination precipitated calciumcarbonate, hydrated alumina, fumed silica, calcium hydroxide, and carbonblack. Inorganic filler can improve the tensile strength of a curedcomposition.

Compositions provided by the present disclosure can comprise, forexample, from 3 wt % to 23 wt % of an inorganic filler or combination ofinorganic fillers, from 5 wt % to 21 wt %, from 8 wt % to 18 wt %, from10 wt % to 16 wt %, or from 11 wt % to 15 wt %, where wt % is based onthe total weight of the composition.

Compositions and sealants provided by the present disclosure can includean adhesion promoter or combination of adhesion promoters.

Low density compositions provided by the present disclosure can comprisean adhesion promoter or combination of adhesion promoters. An adhesionpromoter can include a phenolic adhesion promoter, a combination ofphenolic adhesion promoters, an organo-functional silane, a combinationof organo-functional silanes, or a combination of any of the foregoing.An organosilane can be an amine-functional silane.

Compositions and sealants provided by the present disclosure cancomprise a phenolic adhesion promoter, an organosilane, or a combinationthereof. A phenolic adhesion promoter can comprise a cooked phenolicresin, an un-cooked phenolic resin, or a combination thereof. Examplesof suitable adhesion promoters include phenolic resins such as Methylon®phenolic resin, and organosilanes, such as epoxy-, mercapto- oramine-functional silanes, such as Silquest® organosilanes.

Phenolic adhesion promoters can comprise the reaction product of acondensation reaction of a phenolic resin with one or morethiol-terminated polysulfides. Phenolic adhesion promoters can bethiol-terminated.

Examples of phenolic resins include 2-(hydroxymethyl)phenol,(4-hydroxy-1,3-phenylene)dimethanol, (2-hydroxybenzene-1,3,4-triyl)trimethanol, 2-benzyl-6-(hydorxymethyl)phenol,(4-hydroxy-5-((2-hydroxy-5-(hydroxymethyl)cyclohexa-2,4-dien-1-yl)methyl)-1,3-phenylene)dimethanol,(4-hydroxy-5-((2-hydroxy-3,5-bis(hydroxymethyl)cyclohexa-2,4-dien-1-yl)methyl)-1,3-phenylene)dimethanol,and a combination of any of the foregoing.

Suitable phenolic resins can be synthesized by the base-catalyzedreaction of phenol with formaldehyde.

Examples of suitable polysulfides include Thioplast® resins (AkzoNobel)such as Thioplast® G10, Thioplast® G112, Thioplast® G131, Thioplast® G1,Thioplast® G12, Thioplast® G21, Thioplast® G22, Thioplast® G44, andThioplast® G4.

A thiol-terminated polysulfide can also comprise the reaction product ofa dithiol and a Thioplast® resin. Examples of suitable dithiols includedimercaptodiethylsulfide, dimercaptodioxaoctane,1,5-dimercapto-3-oxapentane, HS—CH₂CH(CH₃)—S—CH₂CH₂—SH,HS—CH(CH₃)CH₂—S—CH₂CH₂—SH, HS—CH₂CH(CH₃)—S—CHCH₃CH₂—SH, andHS—CH(CH₃)CH₂—S—CH₂CH(CH₃)—SH.

Phenolic adhesion promoters can comprise the reaction product of acondensation reaction of a Methylon® resin, a Varcum® resin, or a Durez®resin available from Durez Corporation with a thiol-terminatedpolysulfide such as a Thioplast® resin.

Examples of Methylon® resins include Methylon® 75108 (allyl ether ofmethylol phenol, see U.S. Pat. No. 3,517,082) and Methylon® 75202.

Examples of Varcum® resins include Varcum® 29101, Varcum® 29108, Varcum®29112, Varcum® 29116, Varcum® 29008, Varcum® 29202, Varcum® 29401,Varcum® 29159, Varcum®29181, Varcum® 92600, Varcum® 94635, Varcum®94879, and Varcum® 94917.

An example of a Durez® resin is Durez® 34071.

Compositions provided by the present disclosure can comprise anorgano-functional adhesion promoter such as an organo-functional silane.An organo-functional silane can comprise hydrolysable groups bonded to asilicon atom and at least one organofunctional group. Anorgano-functional silane can have the structureR″—(CH₂)_(n)—Si(—OR)_(3-n)R′_(n), where R″ is an organofunctional group,n is 0, 1, or 2, and R is alkyl such as methyl or ethyl. Examples oforganofunctional groups include epoxy, amino, methacryloxy, or sulfidegroups. An organofunctional silane can be a dipodal silane having two ormore silane groups, a functional dipodal silane, a non-functionaldipodal silane or a combination of any of the foregoing. Anorganofunctional silane can be a combination of a monosilane and adipodal silane.

Compositions provided by the present disclosure can comprise, forexample, from 1.5 wt % to 4 wt % of an adhesion promoter, from 1.7 wt %to 3.8 wt %, from 1.9 wt % to 3.6 wt % to 2.1 wt % to 3.4 wt % from 2.3wt % to 3.2 wt %, from 2.5 wt % to 3.0 wt %, from 2.0 wt % to 4 wt %, orfrom 2.5 wt % to 4 wt % of an adhesion promoter, where wt % is based onthe total weight of the composition.

Low density compositions can comprise, for example, from 1.8 wt % to 3.8wt % of an adhesion promoter, from 2.0 wt % to 3.6 wt %, from 2.2 wt %to 3.4 wt %, from 2.4 wt % to 3.2 wt %, from 2.6 wt % to 3.0 wt % of anadhesion promoter or combination of adhesion promoters, where wt % isbased on the total weight of a composition.

Compositions provided by the present disclosure can comprise an adhesionpromoter comprising a phenolic adhesion promoter or combination ofphenolic adhesion promoters, and an amine-functional silane orcombination of amine-functional silanes.

An adhesion promoter can comprise, for example, from 45 wt % to 65 wt %of a phenolic adhesion promoter; and from 35 wt % to 55 wt % of anamine-functional silane, where wt % is based on the total weight of theadhesion promoter in a composition.

An adhesion promoter can comprise, for example, from 44 wt % to 64 wt %of a phenolic adhesion promoter, and from 36 wt % to 56 wt % of anorganosilane, such as from 50 wt % to 58 wt % of a phenolic adhesionpromoter and from 41 wt % to 51 wt % of an organosilane, where wt % isbased on the total weight of the adhesion promoter in a composition.

In comparison, a typical sealant composition can comprise less than 0.5wt % of adhesion promoters, such as less than 0.2 wt %, where wt % isbased on the total weight of the composition.

An amine-functional silane can comprise a primary amine-functionalsilane, a secondary amine-functional silane, or a combination thereof. Aprimary amine-functional silane refers to a silane having primary aminogroup. A secondary amine-functional silane refers to a silane having asecondary amine group. An amine-functional silane can comprise, forexample, from 40 wt % to 60 wt % of a primary amine-functional silane;and from 40 wt % to 60 wt % of a secondary amine-functional silane; from45 wt % to 55 wt % of a primary amine-functional silane and from 45 wt %to 55 wt % of a secondary amine-functional silane; or from 47 wt % to 53wt % of a primary amine-functional silane and from 47 wt % to 53 wt % ofa secondary amine-functional silane; where wt % is based on the totalweight of the amine-functional silane in a composition.

The ratio of amine equivalents derived from the primary amine-functionalsilane and the secondary amine-functional silane can be, for example,from 1.2:1 to 1:1.2, from 1.1:1 to 1:1.1, or from 1.05:1 to 1:1.05.

A secondary amine-functional silane can be a sterically hinderedamine-functional silane. In a sterically hindered amine-functionalsilane the secondary amine can be proximate a large group or moiety thatlimits or restricts the degrees of freedom of the secondary aminecompared to the degrees of freedom for a non-sterically hinderedsecondary amine. For example, in a sterically hindered secondary amine,the secondary amine can be proximate a phenyl group, a cyclohexyl group,or a branched alkyl group.

Amine-functional silanes can be monomeric amine-functional silaneshaving a molecular weight, for example, from 100 Daltons to 1000Daltons, from 100 Daltons to 800 Daltons, from 100 Daltons to 600Daltons, or from 200 Daltons to 500 Daltons.

Examples of suitable primary amine-functional silanes include4-aminobutyltriethoxysilane, 4-amino-3,3-dimethylbutyltrimethoxysilane,A-(2-aminoethyl)-3-aminopropyltriethoxysilane,3(m-aminophenoxy)propyltrimethoxysilane, m-aminophenyltrimethoxysilane,p-aminophenyltrimethoxysilane, 3-aminopropyltriethoxysilane,3-aminopropyltrimethoxysilane,3-aminopropyltris(methoxyethoxyethoxy)silane,11-aminoundecyltriethoxysilane, 2-(4-pyridylethyl)triethoxysilane,2-(2-pyridylethyltrimethoxysilane, IV-(3-trimethoxysilylpropyl)pyrrole,3-aminopropylsilanetriol,4-amino-3,3-dimethylbutylmethyldimethoxysilane,3-aminopropylmethyldiethoxysilane,1-amino-2-(dimethylethoxysilyl)propane, 3-aminopropyldiisopropyleneethoxysilane, and 3-aminopropyldimethylethoxysilane.

Examples of suitable diamine-functional silanes includeaminoethylaminomethyl)phenethyltrimethoxysilane andN-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

Examples of suitable secondary amine-functional silanes include3-(N-allylamino)propyltrimethoxysilane,n-butylaminopropyltrimethoxysilane,tert-butylaminopropyltrimethoxysilane,(N,N-cylohexylaminomethyl)methyldicthoxysilanc,(N-cyclohexylaminomethyl)triethoxysilane,(IV-cyclohexylaminopropyl)trimethoxysilane,(3-(n-ethylamino)isobutyl)methyldiethoxysilane,(3-(IV-ethylamino)isobutyl)trimethoxysilane,N-methylaminopropylmethyldimethoxysilane,A-methylaminopropyltrimethoxysilane,(phenylaminomethyl)methyldimethoxysilane,A-phenylaminomethyltriethoxysilane, andN-phenylaminopropyltrimethoxysilane.

Suitable amine-functional silanes are commercially available, forexample, from Gelest Inc. and from Dow Corning Corporation.

Compositions provided by the present disclosure can comprise a reactivediluent or combination of reactive diluents. A reactive diluent can beused to reduce the viscosity of the composition. A reactive diluent canbe a low molecular weight monoepoxide, a low molecular weightpolyepoxide such as a diepoxide, or a combination thereof.

Compositions provided by the present disclosure can comprise, forexample, from 0.1 wt % to 4 wt % of a reactive diluent, from 0.2 wt % to3.5 wt %, from 0.3 wt % to 2 wt %, from 0.4 wt % to 1.5 wt %, or from0.5 wt % to 1.5 wt %, where wt % is based on the total weight of thecomposition.

Reactive diluents can be, for example, aliphatic, aromatic, orcycloaliphatic.

A reactive diluent can be an epoxy-functional reactive diluent such as apoly epoxide. Epoxy-functional reactive diluents can comprise lowviscosity glycidyl ethers that can react with the thiol-terminatedpolythioether to become part of the cross-linked cured composition.

For example, a polyepoxide reactive diluent can be a diepoxide orcombination of diepoxides.

Suitable diepoxide reactive diluents include aliphatic diepoxides.

Examples of suitable epoxy-functional reactive diluents includeneopentyl glycol diglycidyl ether, butyl glycidyl ether,trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether,trimethylolethane triglycidyl ether, 1,4-butanediol diglycidyl ether,2-ethylhexyl glycidyl ether, glycidyl ester of neodecanoic acid,glycidyl ester of dimer acid, C₁₂₋₁₄ aliphatic glycidyl ether,cyclohexanedimethanol diglycidyl ether, castor oil triglycidyl ether,propoxylated glycerin triglycidyl ether, propoxylated glycerintriglycidyl ether, propylene glycol diglycidyl ether, O-cresyl glycidylether, p-tertiary butyl phenyl glycidyl ether, noryl phenyl glycidylether, phenyl glycidyl ether, 1,4-butanediol diglycidyl ether,1,6-hexane diol diglycidyl ether, cyclohexane dimethanol, neopentylglycol diglycidyl ether, polypropylene glycol diglycidyl ether,dipropylene glycoldiglycidyl ether, pentaerythritol based polyglycidylether, 1,3-bis(2,3-epoxypropoxy)2,2-dimethylpropane, oxirane-mono[(C₈₋₁₀alkoxy)-methyl]derivatives, alkyl (C₁₂₋₁₄) glycidyl ether,1,2-epoxy-3-(2-methylphenoxy)propane, 1,4-bis(2,3-epoxy(propyloxy)butane, trimethylopropane-epichlorohydrin copolymer,ethylhexylglycidyl ether, 1,4-butanediol-diglycidyl ether, polyglycerol-3-glycidyl ether, glycerol-triglycidyl ether,neopentylglycol-diglycidyl ether, polypropyleneglycol-diglycidyl ether,and trimethylolpropane-triglycidyl ether.

Examples of suitable diepoxides useful as reactive diluents include,include (poly)ethylene glycol diglycidyl ether, (poly)propylene glycoldiglycidyl ether, butanediol diglycidyl ether, and neopentyl glycoldiglycidyl ether; and examples of a suitable triperoxide compoundsinclude trimethylolpropane triglycidyl ether and glycerin triglycidylether.

Other suitable diexpoxides include trishydroxyl phenyl ethane,resorcinol diglycidyl ether, hydrogenated bisphenol A diglycidyl ether,hexahydrophthalic acid diglycidyl ether, glycidyl amine ofm-xylenediamine, modified bisphenol A diglycidyl ether, n-1,4-butanedioldiglycidyl ether, 1,4-cyclohexane di methanol diglycidyl ether,neopentyl glycol diglycidyl ether, dipropylene glycol diglycidyl ether,polypropylene glycol(400) diglycidyl ether, 1,6-hexanediol diglycidylether, ethylene glycol diglycidyl ether, trimethylol propane triglycidylether, trimethylol ethane triglycidyl ether, Castor oil glycidyl ether,propoxylated glycol triglycidyl ether, polyglycerol-3-polyglycidylether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether,or a combination of any of the foregoing.

A reactive diluent can have a molecular weight, for example, from 100Daltons to 1000 Daltons, from 100 Daltons to 800 Daltons, from 100Daltons to 600 Daltons, or from 200 Daltons to 500 Daltons. A reactivediluent such as a diglycidyl ether can have an epoxy equivalent weightfrom 100 g/eq to 200 g/eq, from 100 g/eq to 160 g/eq, from 110 g/eq to150 g/eq or from 120 g/eq to 140 g/eq. A reactive dilute diluent such asa diglycidyl ether can have a viscosity from 5 cps to 50 cps, from 10cps to 40 cps, from 10 cps to 30 cps, or from 10 cps to 20 cps. Areactive diluent such as a diglycidyl ether can be characterized by aviscosity from 5 cps to 30 cps, from 6 cps to 25 cps, from 7 cps to 10cps, or from 10 cps to 18 cps, at 25° C.

Low density sealant compositions provided by the present disclosurecomprise low density microcapsules. A low density microcapsule cancomprise a thermally expandable microcapsule.

A thermally expandable microcapsule refers to a hollow shell comprisinga volatile material that expands at a predetermined temperature.Thermally expandable thermoplastic microcapsules can have an averageinitial particle size of 5 μm to 70 μm, in some cases 10 μm to 24 μm, orfrom 10 μm to 17 μm. The term “average initial particle size” refers tothe average particle size (numerical weighted average of the particlesize distribution) of the microcapsules prior to any expansion. Theparticle size distribution can be determined using a Fischer Sub-SieveSizer or by optical inspection.

A thermally expandable thermoplastic microcapsule can comprise avolatile hydrocarbon within a wall of a thermoplastic resin. Examples ofhydrocarbons suitable for use in such microcapsules are include methylchloride, methyl bromide, trichloroethane, dichloroethane, n-butane,n-heptane, n-propane, n-hexane, n-pentane, isobutane, isopentane,iso-octane, neopentane, petroleum ether, and aliphatic hydrocarbonscontaining fluorine, such as Freon™, and combinations of any of theforegoing.

Examples of materials suitable for forming the wall of a thermallyexpandable microcapsule include polymers of vinylidene chloride,acrylonitrile, styrene, polycarbonate, methyl methacrylate, ethylacrylate, and vinyl acetate, copolymers of these monomers, andcombinations of the polymers and copolymers. A crosslinking agent may beincluded with the materials forming the wall of a thermally expandablemicrocapsule.

Examples of suitable thermoplastic microcapsules include Expancel™microcapsules such as Expancel™DE microspheres available from AkzoNobel. Examples of suitable Expancel™ DE microspheres include Expancel™920 DE 40 and Expancel™ 920 DE 80. Suitable low density microcapsulesare also available from Kureha Corporation.

Suitable low density filler such as low density microcapsules can have amean diameter (d0.5), for example, from 1 μm to 100 μm, from 10 μm to 80μm, or from 10 μm to 50 μm, as determined according to ASTM D1475.

Low density filler such as low density microcapsules can becharacterized by a specific gravity within a range from 0.01 to 0.09,from 0.04 to 0.09, within a range from 0.04 to 0.08, within a range from0.01 to 0.07, within a range from 0.02 to 0.06, within a range from 0.03to 0.05, within a range from 0.05 to 0.09, from 0.06 to 0.09, or withina range from 0.07 to 0.09, wherein the specific gravity is determinedaccording to ASTM D1475. Low density filler such as low densitymicrocapsules can be characterized by a specific gravity less than 0.1,less than 0.09, less than 0.08, less than 0.07, less than 0.06, lessthan 0.05, less than 0.04, less than 0.03, or less than 0.02, whereinthe specific gravity is determined according to ASTM D1475.

Low density filler such as low microcapsules can be characterized by amean particle diameter from 1 μm to 100 μm and can have a substantiallyspherical shape. Low density filler such as low density microcapsulescan be characterized, for example, by a mean particle diameter from 10μm to 100 μm, from 10 μm to 60 μm, from 10 μm to 40 μm, or from 10 μm to30 μm, as determined according to ASTM D1475.

Low density filler can comprise uncoated microcapsules, coatedmicrocapsules, or combinations thereof.

Low density filler such as low density microcapsules can compriseexpanded microcapsules or microballoons having a coating of anaminoplast resin such as a melamine resin. Aminoplast resin-coatedparticles are described, for example, in U.S. Pat. No. 8,993,691, whichis incorporated by reference in its entirety. Such microcapsules can beformed by heating a microcapsule comprising a blowing agent surroundedby a thermoplastic shell. Uncoated low density microcapsules can bereacted with an aminoplast resin such as a urea/formaldehyde resin toprovide a coating of a thermoset resin on the outer surface of theparticle.

Low density filler such as low density microcapsules can comprisethermally expandable thermoplastic microcapsules having an exteriorcoating of an aminoplast resin, such as a melamine resin. The coated lowdensity microcapsules can have an exterior coating of a melamine resin,where the coating can have a thickness, for example, less than 2 μm,less than 1 μm, or less than 0.5 μm. The melamine coating on the lightweight microcapsules is believed to render the microcapsules reactivewith the thiol-terminated polythioether prepolymer and/or thepolyepoxide curing agent, which enhances the fuel resistance, andrenders the microcapsules resistant to pressure.

The thin coating of an aminoplast resin can have a film thickness ofless than 25 μm, less than 20 μm, less than 15 μm, or less than 5 μm.The thin coating of an aminoplast resin can have a film thickness of atleast 0.1 nanometers, such as at least 10 nanometers, or at least 100nanometers, or, in some cases, at least 500 nanometers.

Aminoplast resins can be based on the condensation products offormaldehyde, with an amino- or amido-group carrying substance.Condensation products can be obtained from the reaction of alcohols andformaldehyde with melamine, urea or benzoguanamine. Condensationproducts of other amines and amides can also be employed, for example,aldehyde condensates of triazines, diazines, triazoles, guanidines,guanamines and alkyl- and aryl-substituted derivatives of suchcompounds, including alkyl- and aryl-substituted ureas and alkyl- andaryl-substituted melamines. Examples of such compounds includeN,N′-dimethyl urea, benzourea, dicyandiamide, formaguanamine,acetoguanamine, glycoluril, ammeline,2-chloro-4,6-diamino-1,3,5-triazine,6-methyl-2,4-diamino-1,3,5-triazine, 3,5-diaminotriazole,triaminopyrimidine, 2-mercapto-4,6-diaminopyrimidine and3,4,6-tris(ethylamino)-1,3,5 triazine. Suitable aminoplast resins canalso be based on the condensation products of other aldehydes such asacetaldehyde, crotonaldehyde, acrolein, benzaldehyde, furfural, andglyoxal.

An aminoplast resin can comprise a highly alkylated, low-iminoaminoplast resin which has a degree of polymerization less than 3.75,such as less than 3.0, or less than 2.0. The number average degree ofpolymerization can be defined as the average number of structural unitsper polymer chain. For example, a degree of polymerization of 1.0indicates a completely monomeric triazine structure, while a degree ofpolymerization of 2.0 indicates two triazine rings joined by a methyleneor methylene-oxy bridge. Degree of polymerization represents an averagedegree of polymerization value as determined by gel permeationchromatography using polystyrene standards.

An aminoplast resin can contain methylol or other alkylol groups, and atleast a portion of the alkylol groups can be etherified by reaction withan alcohol. Examples of suitable monohydric alcohols include alcoholssuch as methanol, ethanol, propanol, butanol, pentanol, hexanol,heptanol, benzyl alcohol, other aromatic alcohols, cyclic alcohols suchas cyclohexanol, monoethers of glycols, and halogen-substituted or othersubstituted alcohols, such as 3-chloropropanol and butoxyethanol.Aminoplast resins can be substantially alkylated with methanol orbutanol.

An aminoplast resin can comprise a melamine resin. Examples of suitablemelamine resins include methylated melamine resins(hexamethoxymethylmelamine), mixed ether melamine resins, butylatedmelamine resins, urea resins, butylated urea resins, benzoguanamine andglycoluril resins, and formaldehyde free resins. Such resins areavailable, for example, from Allnex Group and Hexion. Examples ofsuitable melamine resins include methylated melamine resins such asCYMEL™ 300, CYMEL™ 301, CYMEL™ 303LF, CYMEL™ 303ULF, CYMEL™ 304, CYMEL™350, CYMEL 3745, CYMEL™ XW-3106, CYMEL™ MM-100, CYMEL™ 370, CYMEL™ 373,CYMEL™ 380, ASTRO MEL™601, ASTRO MEL™ 601ULF, ASTRO MEL™400, ASTRO MEL™NVV-3A, Aricel PC-6 A, ASTRO MEL™ CR-1, and ASTRO SET™ 90.

A suitable aminoplast resin can comprise a urea-formaldehyde resin.

Aminoplast resin-coated particles are distinct from uncoated particlesthat are merely incorporated into a polymer network, such as is the casewhen uncoated low density particles are dispersed in a film-formingbinder. For aminoplast resin-coated particles, a thin film is depositedon the exterior surface of individual discrete particles such asthermally expanded microcapsules. These aminoplast resin-coatedparticles may then be dispersed in a film-forming binder, therebyresulting in dispersion of the coated particles throughout a polymernetwork. The thin coating of an aminoplast resin can cover, for examplefrom 70% to 100%, from 80% to 100%, or from 90% to 100% of the exteriorsurface of a low density particle such as a thermally expandedmicrocapsule. The coating of an aminoplast resin can form asubstantially continuous covering on the exterior surface of a lowdensity particle.

The low density microcapsules can be prepared by any suitable technique,including, for example, as described U.S. Pat. Nos. 8,816,023 and8,993,691, each of which is incorporated by reference in its entirety.Coated low density microcapsules can be obtained, for example, bypreparing an aqueous dispersion of microcapsules in water with amelamine resin, under stirring. A catalyst may then be added and thedispersion heated to, for example, a temperature from 50° C. to 80° C.Low density microcapsules such as thermally expanded microcapsuleshaving a polyacrylonitrile shell, de-ionized water and an aminoplastresin such as a melamine resin can be combined and mixed. A 10% w/wsolution of para-toluene sulfuric acid in distilled water can then beadded and the mixture reacted at 60° C. for about 2 hours. Saturatedsodium bicarbonate can then be added and the mixture stirred for 10minutes. The solids can be filtered, rinsed with distilled water, anddried overnight at room temperature. The resulting powder of aminoplastresin-coated microcapsules can then be sifted through a 250 μm sieve toremove and separate agglomerates.

Prior to application of an aminoplast resin coating, athermally-expanded thermoplastic microcapsule can be characterized by aspecific gravity, for example, within a range from 0.01 to 0.05, withina range from 0.015 to 0.045, within a range from 0.02 to 0.04, or withina range from 0.025 to 0.035, wherein the specific gravity is determinedaccording to ASTM D1475. For example, Expancel™920 DE 40 and Expancel™920 DE 80 can be characterized by a specific gravity of about 0.03,wherein the specific gravity is determined according to ASTM D1475.

Following coating with an aminoplast resin, an aminoplast-coatedmicrocapsule can be characterized by a specific gravity, for example,within a range from 0.02 to 0.08, within a range from 0.02 to 0.07,within a range from 0.02 to 0.06, within a range from 0.03 to 0.07,within a range from 0.03 to 0.065, within a range from 0.04 to 0.065,within a range from 0.045 to 0.06, or within a range from 0.05 to 0.06,wherein the specific gravity is determined according to ASTM D1475.

Compositions provided by the present disclosure can be formulated foruse as aerospace sealants.

Low density compositions can comprise, for example, from 50 wt % to 70wt % of a thiol-terminated polythioether prepolymer, from 53 wt % to 69wt %, from 55 wt % to 67 wt %, from 57 wt % to 65 wt %, or from 59 wt %to 63 wt % of a thiol-terminated polythioether prepolymer, where wt % isbased on the total weight of the composition.

Low density compositions can comprise, for example, from 13 wt % to 23wt % of a poly epoxide, from 14 wt % to 22 wt %, from 15 wt % to 21 wt%, from 16 wt % to 20 wt %, from 17 wt % to 19 wt % of a poly epoxide,where wt % is based on the total weight of the composition.

Low density compositions can comprise, for example, from 6 wt % to 18 wt% of an inorganic filler, from 7 wt % to 17 wt %, from 8 wt % to 16 wt%, from 9 wt % to 15 wt %, from 10 wt % to 14 wt %, or from 11 wt % to13 wt % of an inorganic filler, where wt % is based on the total weightof the composition.

Low density compositions can comprise, for example, from 2.6 wt % to 4.0wt % of low density microcapsules, from 2.6 wt % to 3.8 wt %, from 2.7wt % to 3.6 wt %, from 2.8 wt % to 3.5 wt %, from 2.9 wt % to 3.4 wt %,or from 3.0 wt % to 3.3 wt %, of low density microcapsules, where wt %is based on the total weight of the composition.

Low density compositions can comprise, for example, from 50 wt % to 70wt % of a thiol-terminated polythioether prepolymer, from 13 wt % to 23wt % of a polyepoxide; and from 2.7 wt % to 4.0 wt % of low densitymicrocapsules, where wt % is based on the total weight of thecomposition.

Low density compositions can comprise, for example, from 53 wt % to 67wt % of a thiol-terminated polythioether prepolymer, from 14 wt % to 22wt % of a polyepoxide; and from 2.8 wt % to 3.8 wt % of low densitymicrocapsules, where wt % is based on the total weight of thecomposition.

Low density compositions can comprise, for example, from 55 wt % to 65wt % of a thiol-terminated polythioether prepolymer, from 15 wt % to 21wt % of a polyepoxide; and from 2.9 wt % to 3.8 wt % of low densitymicrocapsules, where wt % is based on the total weight of thecomposition.

Low density compositions can comprise, for example, from 57 wt % to 63wt % of a thiol-terminated polythioether prepolymer, from 16 wt % to 20wt % of a polyepoxide; and from 2.9 wt % to 3.3 wt % of low densitymicrocapsules, where wt % is based on the total weight of thecomposition.

Low density compositions can comprise, for example, from 59 wt % to 61wt % of a thiol-terminated polythioether prepolymer, from 17 wt % to 19wt % of a polyepoxide; and from 2.9 wt % to 3.2 wt % of low densitymicrocapsules, where wt % is based on the total weight of thecomposition.

Low density compositions can comprise, for example, from 51 wt % to 69wt % of a thiol-terminated polythioether prepolymer, from 13 wt % to 23wt % of a polyepoxide; from 6 wt % to 18 wt % of an inorganic filler;and from 2.7 wt % to 4.0 wt % of low density microcapsules, where wt %is based on the total weight of the composition.

Low density compositions can comprise, for example, from 53 wt % to 67wt % of a thiol-terminated polythioether prepolymer, from 14 wt % to 22wt % of a polyepoxide; from 7 wt % to 17 wt % of an inorganic filler;and from 2.8 wt % to 3.8 wt % of low density microcapsules, where wt %is based on the total weight of the composition.

Low density compositions can comprise, for example, from 55 wt % to 65wt % of a thiol-terminated polythioether prepolymer, from 15 wt % to 21wt % of a polyepoxide; from 8 wt % to 16 wt % of an inorganic filler;and from 2.9 wt % to 3.8 wt % of low density microcapsules, where wt %is based on the total weight of the composition.

Low density compositions can comprise, for example, from 57 wt % to 63wt % of a thiol-terminated polythioether, from 16 wt % to 20 wt % of apoly epoxide; from 9 wt % to 15 wt % of an inorganic filler; and from2.9 wt % to 3.3 wt % of low density microcapsules, where wt % is basedon the total weight of the composition.

Low density compositions can comprise, for example, from 59 wt % to 61wt % of a thiol-terminated polythioether prepolymer, from 17 wt % to 19wt % of a polyepoxide; from 10 wt % to 13 wt % of an inorganic filler;and from 2.9 wt % to 3.2 wt % of low density microcapsules, where wt %is based on the total weight of the composition.

The amount of low density microcapsules in compositions provided by thepresent disclosure can also be characterized in terms of vol %, wherevol % refers to the amount of low density microcapsules with respect tothe total volume of a composition. The vol % of each of the componentsof a composition can be derived from the wt % and density of each of thecomponents as is well known in the art. The vol % of a component such asa low density filler can be estimated from the specific gravity of thecomposition and the specific gravity of the component such as a lowdensity filler, and the wt % of the component in the composition. Forexample, for a composition having specific gravity of 0.77 comprising alow density filler having a specific gravity of 0.056, and thecomposition contains 3.15 wt % of the filler, the composition will haveabout 43 vol % of the low density filler (3.15×(0.77/0.056)).

For example, low density compositions of the present disclosure cancomprise from 30 vol % to 60 vol % of low density microcapsules, from 35vol % to 55 vol %, from 40 vol % to 50 vol %, or from 42 vol % to 48 vol% of low density microcapsules, where vol % is based on the total volumeof the composition.

To achieve low specific gravity sealants, the wt % and the vol % of thelight weight filler in the sealant composition must be increasedsubstantially compared to light weight sealants having a specificgravity of 1 or more. For example, the low specific gravity sealantcompositions provided by the present disclosure having a specificgravity of around 0.75, have a light weight particle content from about45 vol % to about 50 vol %. As a consequence the vol % of the polymericbinder in the composition is substantially reduced and the interfacialsurface area between the filler and the binder is substantiallyincreased.

Uncured low density sealant compositions provided by the presentdisclosure can have from 1.1 equivalents epoxy to 1.3 equivalents epoxyto the thiol equivalents, such as from 1.1 to 1.25 equivalents epoxy,from 1.1 to 1.2, or from 1.1 to 1.15 equivalents epoxy to thiol.

Compositions provided by the present disclosure can comprise, forexample, from 50 wt % to 70 wt % of a thiol-terminated polythioether,from 1 wt % to 5 wt % of an adhesion promoter, from 8 wt % to 18 wt % ofan inorganic filler, from 2.6 wt % to 4.0 wt % of a low density filler,from 13 wt % to 23 wt % of a polyepoxide, and from 0.1 wt % to 2 wt % ofa reactive diluent, wherein wt % is based on the total weight of thecomposition. In the preceding compositions, the compositions cancomprise, for example, from 0.5 wt % to 2.5 wt % of a phenolic adhesionpromoter, and from 0.5 wt % to 2.5 wt % of an organo-functional silane;and from 0.5 wt % to 2 wt % of a polyepoxide having an epoxyfunctionality from 2.5 to 3, and from 13 wt % to 21 wt % of adifunctional poly epoxide such as a hydroxyl-functional difunctionalpolyepoxide, where wt % is based on the total weight of the composition.

Compositions provided by the present disclosure can comprise, forexample, from 56 wt % to 66 wt % of a thiol-terminated polythioether,from 2 wt % to 4 wt % of an adhesion promoter, from 10 wt % to 14 wt %of an inorganic filler, from 2 wt % to 4 wt % of a low density filler,from 16 wt % to 20 wt % of a poly epoxide, and from 0.5 wt % to 1.5 wt %of a reactive diluent, wherein wt % is based on the total weight of thecomposition. In the preceding compositions, the compositions cancomprise, for example, from 1.0 wt % to 2.0 wt % of a phenolic adhesionpromoter, and from 1.0 wt % to 2.0 wt % of an organo-functional silane;and from 1.0 wt % to 1.5 wt % of a polyepoxide having an epoxyfunctionality from 2.5 to 3.2, and from 15 wt % to 19 wt % of adifunctional poly epoxide such as a hydroxyl-functional difunctionalpolyepoxide, where wt % is based on the total weight of the composition.

Compositions such as sealants provided by the present disclosure mayfurther comprise one or more additives such as a curing catalyst, aplasticizer, a reactive diluent, a solvent, or a combination of any ofthe foregoing.

Compositions provided by the present disclosure can include one or morecatalysts.

A suitable catalyst can accelerate the reaction between thiol groups andepoxy groups, and can include, for example, an amine catalyst.

A suitable amine catalyst for use in compositions of the presentdisclosure is capable of catalyzing the reaction between thiol and epoxygroups.

Examples of suitable amine catalysts include tertiary amine catalystssuch as NN-dimethylethanolamine, triethylene diamine (TEDA),bis(2-dimethylaminoethyl)ether (BDMAE), N-ethylmorpholine,N′,N′-dimethylpiperazine, N,N,N′,N′,N′-pentamethyl-diethylene-triamine(PMDETA), N,N-dimethylcyclohexylamine (DMCHA), N,N-dimethylbenzylamine(DMBA), N,N-dimethylcetylamine,N,N,N′N″,N″-pentamethyl-dipropylene-triamine (PMDPTA), triethylamine,1-(2-hydroxypropyl)imidazole, 1,4-diazabicyclo[2.2.2]octane (DABCO®),and DMP-30® (an accelerant composition including2,4,6-tris(dimethylaminomethyl) phenol), dimethylethanolamine (DMEA),bis-(2-dimethylaminoethyl)ether, A-ethylmorpholine, triethylamine,1,8-diazabicyclo[5.4.0]undecene-7 (DBU), benzyldimethylamine (BDMA),N,N,N′-trimethyl-N′-hydroxyethyl-bis(aminoethyl)ether, andN′-(3-(dimethylamino)propyl)-A, A-dimethyl-1,3-propanediamine.

A catalyst can comprise an imidazole catalyst. Examples of suitableimidazole catalysts include imidazole, 2-methylimidazole,2-ethylimidazole, 2-isopropylimidazole, 2-undecylimidazole,2-dodecylimidazole, 2-phenylimidazole, 2-ethyl-4-methyl-imidazole,2-benzylimidazole, 2,4,5-trimethylimidazole, and a combination of any ofthe foregoing.

Other examples of suitable imidazoles include substituted imidazolessuch as alkyl-substituted imidazoles include 2-methyl imidazole,2-ethyl-4-methylimidazole, 2,4-dimethylimidazole, butylimidazole,2-heptadecenyl-4-methylimidazole, 2-undecenylimidazole,1-vinyl-2-methylimidazole, 2-n-heptadecylimidazole, 2-undecylimidazole,2-heptadecylimidazole, 1-benzyl-2-methylimidazole,1-propyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole,1-cyanoethyl-1-cyanoethyl-2-undecylimidazole,1-cyanoethyl-2-phenylimidazole, 1-guanaminoethyl-2-methylimidazole andaddition products of an imidazole and trimellitic acid,2-n-heptadecyl-4-methylimidazole; and aryl-substituted imidazolesincluding phenylimidazole, benzylimidazole,2-methyl-4,5-diphenylimidazole, 2,3,5-triphenylimidazole,2-styrylimidazole, 1-(dodecyl benzyl)-2-methylimidazole,2-(2-hydroxyl-4-t-butylphenyl)-4,5-diphenylimidazole,2-(2-methoxyphenyl)-4,5-diphenylimidazole,2-(3-hydroxyphenyl)-4,5-diphenylimidazole,2-(p-dimethylaminophenyl)-4,5-diphenylimidazole,2-(2-hydroxyphenyl)-4,5-diphenylimidazole,di(4,5-diphenyl-2-imidazole)-benzene-1,4,2-naphthyl-4,5-diphenylimidazole,1-benzyl-2-methylimidazole, and 2-p-methoxystyrylimidazole.

An imidazole catalyst can comprise an imidazole-epoxy adduct. Animidazole-epoxy adduct can be obtained by reacting an imidazole compoundwith an epoxy compound. An imidazole compound can be, for example, anyof those disclosed herein. Examples of suitable epoxy compounds forforming an imidazole-epoxy adduct include 1,2-epoxybutane,1,2-epoxyhexane, 1,2-epoxyoctane, styreneoxide, n-butyl glycidyl ether,hexyl glycidyl ether, phenyl glycidyl ether, glycidyl acetate, glycidylbutyrate, glycidyl hexoate, and glycidyl benzoate. Examples of suitableimidazole-epoxy adducts formed by the addition of an imidazole compoundto an epoxy compound include, for example, NOVACURE™ HX-3722 (anencapsulated imidazole/bisphenol A epoxy adduct dispersed in bisphenol Aepoxy) and NOVACURE™ HX-3921 HP.

A catalyst can comprise a combination of an amine catalyst and animidazole catalyst.

A composition can comprise, for example, from 0.2 wt % to 2 wt % of acatalyst or combination of catalysts, from 0.4 wt % to 1.8 wt %, from0.6 wt % to 1.6 wt %, from 0.8 wt % to 1.4 wt %, or from 0.8 wt % to 1.2wt % of a catalyst or combination of catalysts such as a combination ofan amine catalyst and an imidazole catalyst, where wt % is based on thetotal weight of the composition.

Compositions and sealants provided by the present disclosure cancomprise a plasticizer. A plasticizer can comprise, for example,phthalate esters, chlorinated paraffins, or hydrogenated terphenyls.Examples of suitable plasticizers also include HB-40™ modifiedpolyphenyl and tung oil.

Compositions and sealants provided by the present disclosure cancomprise, for example, less than 2 wt % of a plasticizer, less than 1 wt%, or less than 0.5 wt % of a plasticizer, where wt % is based on thetotal weight of the composition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 15 wt % to 21 wt % of a polyepoxide; and from 35 vol % to 55 vol %of a low density filler, wherein the low density filler comprisesmicrocapsules comprising a coating of an aminoplast resin, wherein wt %is based on the total weight of the composition, and vol % is based onthe total volume of the composition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 15 wt % to 21 wt % of a polyepoxide, wherein the polyepoxidecomprises a diglycidyl ether of bisphenol A and a novolac epoxy resin;and from 35 vol % to 55 vol % of a low density filler, wherein the lowdensity filler comprises microcapsules comprising a coating of anaminoplast resin, wherein wt % is based on the total weight of thecomposition, and vol % is based on the total volume of the composition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 15 wt % to 21 wt % of a polyepoxide, wherein the polyepoxidecomprises a diglycidyl ether of bisphenol A and a novolac epoxy resin;and the polyepoxide comprises at least 85 wt % of the diglycidyl etherof bisphenol A, wherein wt % is based on the total weight of thepolyepoxide; and from 35 vol % to 55 vol % of a low density filler,wherein the low density filler comprises microcapsules comprising acoating of an aminoplast resin, wherein wt % is based on the totalweight of the composition, and vol % is based on the total volume of thecomposition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 15 wt % to 21 wt % of a polyepoxide, wherein the polyepoxidecomprises: from 86 wt % to 99 wt % of the diglycidyl ether of bisphenolA; and from 1 wt % to 11 wt % of the novolac epoxy resin, wherein wt %is based on the total weight of the polyepoxide; and from 35 vol % to 55vol % of a low density filler, wherein the low density filler comprisesmicrocapsules comprising a coating of an aminoplast resin, wherein wt %is based on the total weight of the composition, and vol % is based onthe total volume of the composition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 15 wt % to 21 wt % of a polyepoxide, wherein the polyepoxidecomprises a diglycidyl ether of bisphenol A and a novolac epoxy resin;where the diglycidyl ether of bisphenol A comprises pendent hydroxylgroups; and from 35 vol % to 55 vol % of a low density filler, whereinthe low density filler comprises microcapsules comprising a coating ofan aminoplast resin, wherein wt % is based on the total weight of thecomposition, and vol % is based on the total volume of the composition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 13 wt % to 23 wt % of a polyepoxide; and from 35 vol % to 55 vol %of a low density filler, wherein the low density filler comprisesmicrocapsules comprising a coating of an aminoplast resin; from 6 wt %to 18 wt % of an inorganic filler; from 1.8 wt % to 3.8 wt % of anadhesion promoter; and from 0.2 wt % to 3.0 wt % of an epoxy-functionalreactive diluent, wherein wt % is based on the total weight of thecomposition, and vol % is based on the total volume of the composition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 13 wt % to 23 wt % of a polyepoxide; and from 35 vol % to 55 vol %of a low density filler, wherein the low density filler comprisesmicrocapsules comprising a coating of an aminoplast resin; from 1.8 wt %to 3.8 wt % of an adhesion promoter, wherein the adhesion promotercomprises a phenolic adhesion promoter and an amine-functional silane;and wherein wt % is based on the total weight of the composition, andvol % is based on the total volume of the composition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 13 wt % to 23 wt % of a polyepoxide; and from 35 vol % to 55 vol %of a low density filler, wherein the low density filler comprisesmicrocapsules comprising a coating of an aminoplast resin; from 1.8 wt %to 3.8 wt % of an adhesion promoter, wherein the adhesion promotercomprises from 45 wt % to 65 wt % of the phenolic adhesion promoter, andfrom 35 wt % to 55 wt % of the amine-functional silane, wherein wt % isbased on the total weight of the adhesion promoter; and wherein wt % isbased on the total weight of the composition, and vol % is based on thetotal volume of the composition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 13 wt % to 23 wt % of a polyepoxide; and from 35 vol % to 55 vol %of a low density filler, wherein the low density filler comprisesmicrocapsules comprising a coating of an aminoplast resin; from 1.8 wt %to 3.8 wt % of an adhesion promoter, wherein the adhesion promotercomprises a phenolic adhesion promoter and an amine-functional silane,wherein the amine-functional silane comprises: from 40 wt % to 60 wt %of the primary amine-functional silane; and from 40 wt % to 60 wt % ofthe secondary amine-functional silane, wherein wt % is based on thetotal weight of the amine-functional silane; and wherein wt % is basedon the total weight of the composition, and vol % is based on the totalvolume of the composition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 13 wt % to 23 wt % of a polyepoxide; and from 35 vol % to 55 vol %of a low density filler, wherein the low density filler comprisesmicrocapsules comprising a coating of an aminoplast resin; from 6 wt %to 18 wt % of an inorganic filler; from 1.8 wt % to 3.8 wt % of anadhesion promoter; and from 0.2 wt % to 3 wt % of an epoxy-functionalreactive diluent, wherein the epoxy-functional reactive diluentcomprises an aliphatic diglycidyl ether, wherein wt % is based on thetotal weight of the composition, and vol % is based on the total volumeof the composition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 13 wt % to 23 wt % of a polyepoxide; and from 35 vol % to 55 vol %of a low density filler, wherein the low density filler comprisesmicrocapsules comprising a coating of an aminoplast resin, wherein wt %is based on the total weight of the composition, and vol % is based onthe total volume of the composition, and wherein the composition ischaracterized by a specific gravity within a range from 0.65 to 0.85,wherein the specific gravity is determined according to ASTM D1475(modified).

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 13 wt % to 23 wt % of a polyepoxide; and from 35 vol % to 55 vol %of a low density filler, wherein the low density filler comprisesmicrocapsules comprising a coating of an aminoplast resin, wherein wt %is based on the total weight of the composition, and vol % is based onthe total volume of the composition, wherein the composition ischaracterized by a specific gravity within a range from 0.65 to 0.85,wherein the specific gravity is determined according to ASTM D1475(modified) and wherein the composition comprises from 2.8 wt % to 4.0 wt% of the low density filler, wherein the low density filler ischaracterized by a specific gravity within a range from 0.01 to 0.09,such as from 0.02 to 0.08, or from 0.03 to 0.06, wherein the specificgravity of the low density filler is determined according to ASTM D1475.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 13 wt % to 23 wt % of a polyepoxide, wherein the polyepoxidecomprises a diglycidyl ether of bisphenol A and a novolac epoxy resin,wherein the composition comprises: from 10 wt % to 25 wt % of adiglycidyl ether of bisphenol A; and from 0.2 wt % to 2 wt % of anovolac epoxy resin; from 2.8 wt % to 4.0 wt % of the low densityfiller, wherein the low density filler is characterized by a specificgravity within a range from 0.01 to 0.09, wherein the specific gravityis determined according to ASTM D1475 from 6 wt % to 18 wt % of aninorganic filler; from 1.8 wt % to 3.8 wt % of an adhesion promoter,wherein the adhesion promoter comprises a phenolic adhesion promoter andan amine-functional silane, wherein the compositions comprise from 1 wt% to 3 wt % of a phenolic adhesion promoter; and from 0.5 wt % to 2 wt %of an amine-functional silane; and from 0.2 wt % to 3 wt % of anepoxy-functional reactive diluent, wherein wt % is based on the totalweight of the composition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 13 wt % to 23 wt % of a polyepoxide, wherein the polyepoxidecomprises a diglycidyl ether of bisphenol A and a novolac epoxy resin,wherein the composition comprises: from 10 wt % to 25 wt % of adiglycidyl ether of bisphenol A; and from 0.2 wt % to 2 wt % of anovolac epoxy resin; from 2.8 wt % to 4.0 wt % of the low densityfiller, wherein the low density filler is characterized by a specificgravity within a range from 0.01 to 0.09, wherein the specific gravityis determined according to ASTM D1475; from 6 wt % to 18 wt % of aninorganic filler; from 1.8 wt % to 3.8 wt % of an adhesion promoter,wherein the adhesion promoter comprises a phenolic adhesion promoter andan amine-functional silane, wherein the composition comprises: from 1 wt% to 3 wt % of a phenolic adhesion promoter; and from 0.5 wt % to 2 wt %of an amine-functional silane, wherein the amine-functional silanecomprises a primary amine-functional silane and a secondaryamine-functional, wherein the compositions comprise from 0.4 wt % to 0.9wt % of a primary amine-functional silane; and from 0.4 wt % to 0.9 wt %of a secondary amine-functional silane; and from 0.2 wt % to 3 wt % ofan epoxy-functional reactive diluent, wherein wt % is based on the totalweight of the composition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 13 wt % to 23 wt % of a polyepoxide, wherein the polyepoxidecomprises a diglycidyl ether of bisphenol A and a novolac epoxy resin,wherein the composition comprises: from 10 wt % to 25 wt % of adiglycidyl ether of bisphenol A; and from 0.2 wt % to 2 wt % of anovolac epoxy resin; from 2.8 wt % to 4.0 wt % of the low densityfiller, wherein the low density filler is characterized by a specificgravity within a range from 0.01 to 0.09, wherein the specific gravityis determined according to ASTM D1475 from 6 wt % to 18 wt % of aninorganic filler; from 1.8 wt % to 3.8 wt % of an adhesion promoter,wherein the adhesion promoter comprises a phenolic adhesion promoter andan amine-functional silane, wherein the compositions comprise from 1 wt% to 3 wt % of a phenolic adhesion promoter; and from 0.5 wt % to 2 wt %of an amine-functional silane; and from 0.2 wt % to 3 wt % of anepoxy-functional reactive diluent, wherein the epoxy-functional reactivediluent comprises an aliphatic diglycidyl ether, wherein wt % is basedon the total weight of the composition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 135 wt % to 23 wt % of a polyepoxide, wherein the polyepoxidecomprises a diglycidyl ether of bisphenol A and a novolac epoxy resin,wherein the composition comprises from 10 wt % to 25 wt % of adiglycidyl ether of bisphenol A, wherein the diglycidyl ether ofbisphenol A comprises pendent hydroxyl groups; and from 0.2 wt % to 2 wt% of a novolac epoxy resin; from 2.8 wt % to 4.0 wt % of the low densityfiller, wherein the low density filler is characterized by a specificgravity within a range from 0.01 to 0.09, wherein the specific gravityis determined according to ASTM D1475 from 6 wt % to 18 wt % of aninorganic filler; from 1.8 wt % to 3.8 wt % of an adhesion promoter,wherein the adhesion promoter comprises a phenolic adhesion promoter andan amine-functional silane, wherein the compositions comprise from 1 wt% to 3 wt % of a phenolic adhesion promoter; and from 0.5 wt % to 2 wt %of an amine-functional silane; and from 0.2 wt % to 3 wt % of anepoxy-functional reactive diluent, wherein wt % is based on the totalweight of the composition.

Compositions provided by the present disclose can comprise, for example,from 50 wt % to 70 wt % of a thiol-terminated polythioether prepolymer;from 13 wt % to 23 wt % of a polyepoxide, wherein the polyepoxidecomprises a diglycidyl ether of bisphenol A and a novolac epoxy resin,wherein the compositions comprise from 10 wt % to 25 wt % of adiglycidyl ether of bisphenol A, wherein the diglycidyl ether ofbisphenol A comprises pendent hydroxyl groups; and from 0.2 wt % to 2 wt% of a novolac epoxy resin; from 2.5 wt % to 4.0 wt % of the low densityfiller, wherein the low density filler is characterized by a specificgravity within a range from 0.01 to 0.09, wherein the specific gravityis determined according to ASTM D1475 from 6 wt % to 18 wt % of aninorganic filler; from 1.8 wt % to 3.8 wt % of an adhesion promoter,wherein the adhesion promoter comprises a phenolic adhesion promoter andan amine-functional silane, wherein the compositions comprise from 1 wt% to 3 wt % of a phenolic adhesion promoter; and from 0.5 wt % to 2 wt %of an amine-functional silane; and from 0.2 wt % to 3 wt % of anepoxy-functional reactive diluent, wherein the epoxy-functional reactivediluent comprises an aliphatic diglycidyl ether, wherein wt % is basedon the total weight of the composition.

Curable sealant systems of the present disclosure can be provided astwo-part sealant compositions. The two-parts can be maintainedseparately and can be combined prior to use. A first part can comprisethiol-terminated polythioether prepolymers, inorganic filler,low-density microcapsules, adhesion promoter, catalyst, and otheradditives. A second part can comprise a polyepoxide curing agent,inorganic filler and other additives. Other additives can includephenolic adhesion promoters, silane adhesion promoters, amine catalysts,plasticizers, pigments, solvents, reactive diluents, and a combinationof any of the foregoing.

Low density sealants provided by the present disclosure can be providedas a two-part sealant composition. The two-parts can be storedseparately and combined and mixed just prior to use.

A first part of a sealant system can comprise the thiol-terminatedpolythioether, adhesion promoter, inorganic filler, curing catalyst, lowdensity microcapsules, and other additives such as plasticizer andsolvent.

A second part of a sealant system can comprise the polyepoxide resin,inorganic filler, and other additives such as pigment, reactive diluent,and adhesion promoter.

The components of the first part of a sealant system and the second partof a sealant system can be selected to separate the reactive componentsand to achieve, for example, desirable rheological properties forstorage stability and to facilitate mixing and homogeneous dispersion ofthe components.

For example, a first part of a sealant system can comprise, for example,from 66 wt % to 86 wt % of a thiol-terminated polythioether prepolymer,from 69 wt % to 83 wt %, or from 71 wt % to 80 wt % of athiol-terminated polythioether prepolymer; from 10 wt % to 20 wt % ofinorganic fillers, from 12 wt % to 18 wt %, or from 14 wt % to 16 wt %of inorganic fillers; and from 2 wt % to 6 wt % of a low densitymicrocapsules, from 3 wt % to 5 wt %, or from 3.5 wt % to 4.5 wt % of alow density microcapsules, wherein wt % is based on the total weight ofthe first part of a sealant system.

A first part of a sealant system can comprise, for example, from 66 wt %to 86 wt % of a thiol-terminated polythioether, from 1 wt % to 7 wt % ofan adhesion promoter, from 10 wt % to 20 wt % of an inorganic filler,and from 2 wt % to 6 wt % of a light weight filler, wherein wt % isbased on the total weight of the first part of a sealant system.

A first part of a sealant system can comprise, for example, from 71 wt %to 81 wt % of a thiol-terminated polythioether, from 3 wt % to 5 wt % ofan adhesion promoter, from 13 wt % to 17 wt % of an inorganic filler,and from 3 wt % to 5 wt % of a light weight filler, wherein wt % isbased on the total weight of the first part of a sealant system.

For example, a second part of a sealant system can comprise, forexample, from 77 wt % to 97 wt % of a polyepoxide, from 80 wt % to 94 wt% or a polyepoxide, or from 83 wt % to 91 wt % of a polyepoxide; andfrom 2.5 wt % to 6.5 wt % or an inorganic filler, from 3 wt % to 6 wt %,or from 3.5 wt % to 5.5 wt % of an inorganic filler, wherein wt % isbased on the total weight of the second part of a sealant system.

A second part of a sealant system can comprise, for example, from 76 wt% to 96 wt % of a polyepoxide, from 2 wt % to 8 wt % or anepoxy-functional reactive diluent, from 1 wt % to 5 wt % of an adhesionpromoter, and from 2 wt % to 8 wt % of an inorganic filler, wherein wt %is based on the total weight of the second part of a sealant system.

A second part of a sealant system can comprise, for example, from 81 wt% to 91 wt % of a polyepoxide, from 4 wt % to 6 wt % or anepoxy-functional reactive diluent, from 2 wt % to 4 wt % of an adhesionpromoter, and from 4 wt % to 6 wt % of an inorganic filler, wherein wt %is based on the total weight of the second part of a sealant system.

A first part of a sealant system can comprise, for example, from 66 wt %to 86 wt % of a thiol-terminated polythioether prepolymer, from 1.7 wt %to 3.7 wt % of an adhesion promoter, from 5 wt % to 25 wt % of aninorganic filler, and from 2 wt % to 5 wt % of low densitymicrocapsules, where wt % is based on the total weight of the first partof a sealant system.

A first part of a sealant system can comprise, for example, from 71 wt %to 81 wt % of a thiol-terminated polythioether prepolymer, from 2.2 wt %to 3.2 wt % of an adhesion promoter, from 10 wt % to 22 wt % of aninorganic filler, and from 3 wt % to 4 wt % of low densitymicrocapsules, where wt % is based on the total weight of the first partof a sealant system.

A second part can comprise, for example, from 77 wt % to 97 wt % of apolyepoxide, from 2 wt % to 4 wt % of an adhesion promoter, and from 3wt % to 6 wt % of an inorganic filler, where wt % is based on the totalweight of the second part.

A second part of a sealant system can comprise, for example, from 82 wt% to 92 wt % of a polyepoxide, from 2.5 wt % to 3.5 wt % of an adhesionpromoter, and from 4 wt % to 5 wt % of an inorganic filler, where wt %is based on the total weight of the second part of a sealant system.

Compositions, including sealants, provided by the present disclosure maybe applied to any of a variety of substrates. Examples of substrates towhich a composition may be applied include metals such as titanium,stainless steel, and aluminum, any of which may be anodized, primed,organic-coated or chromate-coated, epoxy, urethane, graphite, fiberglasscomposite, Kevlar®, acrylics, and polycarbonates. Compositions providedby the present disclosure may be applied to a coating on a substrate,such as a primer coating.

Compositions and sealants provided by the present disclosure may beapplied directly onto the surface of a substrate or over an underlayerby any suitable coating process.

Methods are provided for sealing an aperture and/or surface utilizing acomposition provided by the present disclosure. These methods comprise,for example, applying a composition provided by the present disclosureto an aperture and/or surface, and curing the composition. A method forsealing an aperture and/or surface can comprise applying a sealantcomposition provided by the present disclosure to surfaces defining anaperture and curing the sealant, to provide a sealed aperture and/orsurface. A thickness of an applied composition can range, for example,from 20 mils (0.02 inches) to 0.75 inches, from 0.05 inches to 0.6inches, from 0.1 inches to 0.5 inches, from 0.15 inches to 0.4 inches,or from 0.2 inches to 0.3 inches. A thickness of an applied compositioncan range, for example, from 0.05 cm to 2 cm, from 0.1 cm to 1.5 cm,from 0.2 cm to 1.25 cm, from 0.3 cm to 1.0 cm, from 0.4 cm to 0.9 cm, orfrom 0.5 cm to 0.8 cm.

Composition and sealants may be cured at a temperature from 20° C. to25° C., and atmospheric humidity. A composition may be cured underconditions encompassing a temperature from a 0° C. to 100° C. andhumidity from 0% relative humidity to 100% relative humidity. Acomposition may be cured at a higher temperature such as at least 30°C., at least 40° C., or at least 50° C. A composition may be cured atroom temperature, e.g., 25° C.

When cured at room temperature a sealant provided by the presentdisclosure can cure to a tack free surface, for example, within 24hours, within 20 hours, within 16 hours, within 12 hours, within 6hours, or within 3 hours, from the time of mixing.

Compositions and sealants provided by the present disclosure curerapidly at the end of the working time. For example, a sealant can cure,at room temperature, to a tack free surface within 36 hours after thetime the sealant is no longer workable (end of working time), within 24hours, within 12 hours, within 6 hours, or within 3 hours. A sealant cancure, at room temperature, to a Shore A hardness of 30A, for example,within 24 hours after the time the sealant is no longer workable (end ofworking time), within 12 hours, or within 6 hours.

Sealants provided by the present disclosure can exhibit an applicationtime, for example, of at least 30 minutes, at least 1 hour, at least 2hours, at least 4 hours, or at least 8 hours. The application time isreflected by the extrusion rate such that 2 hours after the twocomponents of the sealant system are mixed the sealant will exhibit anextrusion rate of at least 15 g/min, measured according to AMS 3281 andAMS 3277.

The time to form a viable seal using curable compositions of the presentdisclosure can depend on several factors as can be appreciated by thoseskilled in the art, and as defined by the requirements of applicablestandards and specifications. In general, curable compositions of thepresent disclosure develop adhesion strength within 24 hours to 30hours, and 90% of full adhesion strength develops from 2 days to 3 days,following mixing and application to a surface. In general, full adhesionstrength as well as other properties of cured compositions of thepresent disclosure becomes fully developed within 7 days followingmixing and application of a curable composition to a surface.

Sealants provided by the present disclosure can be used to seal anaperture and/or surface of aviation and aerospace vehicles. The sealantsmay be used to seal apertures and/or surfaces such as aperturesassociated with fuel tanks. To seal an aperture and/or surface a sealantmay be applied to a surface or one or more surfaces defining an apertureand the sealant allowed to cure to seal the aperture and/or surface.

Compositions and sealants provided by the present disclosure arefuel-resistant. As used herein, the term “fuel resistant” means that acomposition, when applied to a substrate and cured, can provide a curedproduct, such as a sealant, that exhibits a percent volume swell of notgreater than 40%, in some cases not greater than 25%, in some cases notgreater than 20%, in yet other cases not more than 10%, after immersionfor one week at 140° F. (60° C.) and ambient pressure in Jet ReferenceFluid (JRF) Type I according to methods similar to those described inASTM D1475 (modified) (American Society for Testing and Materials) orAMS 3269 (Aerospace Material Specification). JRF Type I, as employed fordetermination of fuel resistance, has the following composition:toluene: 28%±1% by volume; cyclohexane (technical): 34%±1% by volume;isooctane: 38%±1% by volume; and tertiary dibutyl disulfide: 1%±0.005%by volume (see AMS 2629, issued Jul. 1, 1989, § 3.1.1 etc., availablefrom Society of Automotive Engineers (SAE)).

A cured sealant comprising a composition provided by the presentdisclosure can meet or exceeds the requirements for aerospace sealantsas set forth in AMS 3277.

A cured sealant comprising a composition provided by the presentdisclosure can meet or exceeds the requirements for aerospace sealantsas set forth in AMS 3281.

Apertures and surfaces, including apertures and surfaces of aerospacevehicles, sealed with compositions provided by the present disclosureare also disclosed.

Aspects of the Present Invention

1. A composition comprising: from 50 wt % to 70 wt % of athiol-terminated polythioether prepolymer; from 15 wt % to 21 wt % of apolyepoxide; and from 35 vol % to 55 vol % of a low density filler,wherein the low density filler is characterized by a specific gravityless than 0.1, wherein wt % is based on the total weight of thecomposition, and vol % is based on the total volume of the composition,and wherein the composition is characterized by a specific gravity lessthan 0.9, wherein the specific gravity is determined according to ASTMD1475 (modified).

2. The composition of aspect 1, wherein when cured, the curedcomposition meets or exceeds the requirements for aerospace sealants asset forth in AMS 3277 and/or AMS 3281.

3. The composition of any one of aspects 1 to 2, wherein the compositionis characterized by a specific gravity within a range from 0.65 to 0.85,wherein the specific gravity is determined according to ASTM D1475(modified).

4. The composition of any one of aspects 1 to 3, wherein thethiol-terminated polythioether prepolymer comprises the chemicalstructure of Formula (1):

$\begin{matrix}{{–R}^{1}{–\left\lbrack {{{–S–}\left( {CH}_{2} \right)}_{2}{{–O–}\left\lbrack {{–R}^{2}{–O–}} \right\rbrack}_{m}{–\left( {CH}_{2} \right)}_{2}{–S–R}^{1}} \right\rbrack}_{n}–} & (1)\end{matrix}$

wherein,

-   -   each R¹ can independently comprise a C₂₋₁₀ n-alkanediyl group, a        C₃₋₆ branched alkanediyl group, a C₆₋₈ cycloalkanediyl group, a        C₆₋₁₀ alkanecycloalkanediyl group, a heterocyclic group, or a        —[(—CHR³—)_(p)—X—]_(q)—(CHR³)_(r)— group, wherein each R³ can        comprise from hydrogen or methyl;    -   each R² can independently comprise a C₂₋₁₀ n-alkanediyl group, a        C₃₋₆ branched alkanediyl group, a C₆₋₈ cycloalkanediyl group, a        C₆₋₁₄ alkanecycloalkanediyl group, a heterocyclic group, or a        —[(—CH₂-)_(p)—X—]_(q)—(CH₂)_(r)— group;    -   each X can independently comprise O, S, and —NR—, wherein R can        comprise from hydrogen or methyl;    -   m ranges from 0 to 50;    -   n is an integer ranging from 1 to 60;    -   p is an integer ranging from 2 to 6;    -   q is an integer ranging from 1 to 5; and    -   r is an integer ranging from 2 to 10.

5. The composition of any one of aspects 1 to 4, wherein thethiol-terminated polythioether prepolymer can comprise athiol-terminated polythioether prepolymer of Formula (2a), athiol-terminated polythioether prepolymer of Formula (2b), or acombination thereof:

$\begin{matrix}{\left( {{HS–}R} \right)^{1}{–\left\lbrack {{{–S–}\left( {CH}_{2} \right)}_{2}{{–O–}\left( {R^{2}{–O}} \right)}_{m}{–\left( {CH}_{2} \right)}_{2}{–S–R}^{1}–} \right\rbrack}_{n}{–SH}} & \left( {2a} \right) \\{\left\{ {\left( {{HS–}R} \right)^{1}{–\left\lbrack {{{–S–}\left( {CH}_{2} \right)}_{2}{{–O–}\left( {R^{2}{–O}} \right)}_{m}{–\left( {CH}_{2} \right)}_{2}{–S–R}^{1}–} \right\rbrack}_{n}{–S–V}^{\prime}–} \right\}_{z}B} & \left( {2b} \right)\end{matrix}$

wherein,

-   -   each R¹ can independently comprise from C₂₋₁₀ alkanediyl, C₆₋₈        cycloalkanediyl, C₆₋₁₄ alkanecycloalkanediyl, C₅₋₈        heterocycloalkanediyl, or —[(—CHR³—)_(p)—X—]_(q)—(—CHR³—)_(r)—,        wherein,        -   p is an integer from 2 to 6;        -   q is an integer from 1 to 5;        -   r is an integer from 2 to 10;        -   each R³ can independently comprise hydrogen or methyl; and        -   each X can independently comprise —O—, —S—, or —NR—, wherein            R can comprise hydrogen or methyl;    -   each R² can independently comprise C₁₋₁₀ alkanediyl, C₆₋₈        cycloalkanediyl, C₆₋₁₄ alkanecycloalkanediyl, or        —[(—CHR³—)_(p)—X—]_(q)—(—CHR³—)_(r)—, wherein p, q, r, R³, and X        are as defined as for R¹;    -   m is an integer from 0 to 50;    -   n is an integer from 1 to 60;    -   B represents a core of a z-valent, polyfunctionalizing agent        B(—V)_(z) wherein,        -   z is an integer from 3 to 6; and        -   each V is a moiety comprising a terminal group reactive with            a thiol; and    -   each —V′— is derived from the reaction of —V with a thiol.

6. The composition of any one of aspects 1 to 5, wherein the polyepoxidecomprises hydantoin diepoxide, a diglycidyl ether of bisphenol-A, adiglycidyl ether of bisphenol-F, a novolac-type polyepoxide, epoxidizedunsaturated phenolic resins, dimer acid-based epoxy resins, or acombination of any of the foregoing.

7. The composition of any one of aspects 1 to 6, wherein the polyepoxidecomprises from 85 wt % to 99 wt % of a diglycidyl ether of bisphenol A,wherein wt % is based on the total weight of the polyepoxide in thecomposition.

8. The composition of any one of aspects 1 to 7, wherein the polyepoxidecomprises from 1 wt % to 11 wt % of a novolac polyepoxide, wherein wt %is based on the total weight of the polyepoxide in the composition.

9. The composition of any one of aspects 1 to 8, wherein the polyepoxidecomprises: from 86 wt % to 99 wt % of a diglycidyl ether of bisphenol A;and from 1 wt % to 11 wt % of a novolac polyepoxide; wherein wt % isbased on the total weight of the polyepoxide in the composition.

10. The composition of any one of aspects 1 to 9, wherein thepolyepoxide comprise a hydroxyl-functional polyepoxide or combination ofhydroxyl-functional polyepoxides.

11. The composition of aspect 10, wherein, the hydroxyl-functionalpolyepoxide comprises a hydroxyl-functional diglycidyl ether ofbisphenol A.

12. The composition of any one of aspects 1 to 11, wherein, thehydroxyl-functional diglycidyl ether of bisphenol A has structure:

wherein n is within a range from 1 to 6.

13. The composition of any one of aspects 1 to 12, wherein thepolyepoxide comprises a difunctional polyepoxide, a trifunctionalpolyepoxide, or a combination of any of the foregoing.

14. The composition of any one of aspects 1 to 13, wherein thecomposition comprises: from 86 wt % to 99 wt % of a difunctionalpolyepoxide; and from 1 wt % to 11 wt % of a trifunctional polyepoxide,wherein wt % is based on the total weight of the polyepoxide in thecomposition.

15. The composition of any one of aspects 1 to 14, wherein thecomposition comprises: a hydroxyl-functional polyepoxide; atrifunctional polyepoxide that does not contain pendent hydroxyl groups;a difunctional poly epoxide that does not contain pendent hydroxylgroups; a hydroxyl-functional trifunctional polyepoxide, or acombination of any of the foregoing.

16. The composition of any one of aspects 1 to 15, wherein thecomposition comprises: from 86 wt % to 99 wt % of a hydroxyl-functionaldifunctional polyepoxide; and from 1 wt % to 11 wt % of a trifunctionalpolyepoxide, wherein wt % is based on the total weight of thepolyepoxide in the composition.

17. The composition of any one of aspects 1 to 16, wherein thecomposition comprises: from 86 wt % to 99 wt % of a hydroxyl-functionaldifunctional polyepoxide; and from 1 wt % to 11 wt % of anon-hydroxyl-functional polyepoxide, wherein wt % is based on the totalweight of the polyepoxide in the composition.

18. The composition of any one of aspects 1 to 17, wherein thepolyepoxide comprises: from 2 wt % to 10 wt % of a polyepoxide having anaverage epoxy functionality from 2.6 to 3.2; and from 90 wt % to 98 wt %of a difunctional polyepoxide; wherein wt % is based on the total weightof the polyepoxide in the composition.

19. The composition of any one of aspects 1 to 18, wherein thepolyepoxide comprises a diglycidyl ether of bisphenol A and a novolacepoxy resin.

20. The composition of any one of aspects 1 to 19, wherein thepolyepoxide comprises at least 85 wt % of a diglycidyl ether ofbisphenol A, wherein wt % is based on the total weight of thepolyepoxide in the composition.

21. The composition of any one of aspects 1 to 20, wherein thepolyepoxide comprises: from 86 wt % to 99 wt % of the diglycidyl etherof bisphenol A; and from 1 wt % to 11 wt % of the novolac epoxy resin,wherein wt % is based on the total weight of the polyepoxide in thecomposition.

22. The composition of aspect 21, wherein the diglycidyl ether ofbisphenol A comprises pendent hydroxyl groups.

23. The composition of any one of aspects 1 to 22, wherein the lowdensity filler is characterized by a mean particle diameter within arange from 1 μm to 100 μm, wherein the mean particle diameter isdetermined according to ASTM D1475

24. The composition of any one of aspects 1 to 23, wherein the lowdensity filler is characterized by a specific gravity within a rangefrom 0.01 to 0.09, wherein the specific gravity is determined accordingto ASTM D1475.

25. The composition of any one of aspects 1 to 24, wherein the lowdensity filler is characterized by a specific gravity within a rangefrom 0.03 to 0.06, wherein the specific gravity is determined accordingto ASTM D1475.

26. The composition of any one of aspects 1 to 25, wherein the lowdensity filler comprises uncoated low density microcapsules, coated lowdensity microcapsules, or a combination thereof.

27. The composition of any one of aspects 1 to 26, wherein the lowdensity filler comprises uncoated low density microcapsules.

28. The composition of aspect 27, wherein the uncoated low densitymicrocapsules are characterized by a specific gravity within a rangefrom 0.01 to 0.05, wherein the specific gravity is determined accordingto ASTM D1475.

29. The composition of any one of aspects 1 to 28, wherein the lowdensity filler comprises coated low density microcapsules.

30. The composition of aspect 29, wherein the coated low densitymicrocapsules comprise a coating of an aminoplast resin.

31. The composition of any one of aspects 29 to 30, wherein the coatedlow density microcapsules comprise a coating of a urea-formaldehyderesin.

32. The composition of any one of aspects 29 to 31, wherein the coatedlow density microcapsules are characterized by a specific gravity withina range from 0.03 to 0.08, wherein the specific gravity is determinedaccording to ASTM D1475.

33. The composition of any one of aspects 1 to 32, wherein thecomposition comprises from 2.8 wt % to 4.0 wt % of the low densityfiller, wherein the low density filler is characterized by a specificgravity within a range from 0.01 to 0.09, wherein the specific gravityis determined according to ASTM D1475.

34. The composition of any one of aspects 1 to 33, wherein thecomposition comprises from 2.8 wt % to 4.0 wt % of the low densityfiller, wherein the low density filler is characterized by a specificgravity within a range from 0.03 to 0.06, wherein the specific gravityis determined according to ASTM D1475.

35. The composition of any one of aspects 1 to 34, further comprising:from 10 wt % to 16 wt % of an inorganic filler; from 1.8 wt % to 3.8 wt% of an adhesion promoter; and from 0.2 wt % to 3 wt % of anepoxy-functional reactive diluent, wherein wt % is based on the totalweight of the composition.

36. The composition of aspect 35, wherein the inorganic filler comprisesprecipitated calcium carbonate, hydrated alumina, fumed silica, calciumhydroxide, carbon black, or a combination off any of the foregoing.

37. The composition of any one of aspects 35 to 36, wherein the adhesionpromoter comprises a phenolic adhesion promoter and an amine-functionalsilane.

38. The composition of any one of aspects 35 to 37, wherein the adhesionpromoter comprises: from 45 wt % to 65 wt % of a phenolic adhesionpromoter; and from 35 wt % to 55 wt % of an amine-functional silane,wherein wt % is based on the total weight of the adhesion promoter inthe composition.

39. The composition of any one of aspects 37 to 38, wherein the phenolicadhesion promoter comprises the reaction product of a condensationreaction of a phenolic resin with one or more thiol-terminatedpolysulfides.

40. The composition of any one of aspects 37 to 39, wherein the phenolicadhesion promoter comprises a thiol-terminated phenolic adhesionpromoter.

41. The composition of any one of aspects 37 to 40, wherein theamine-functional silane comprises; a primary amine-functional silane; asecondary amine-functional silane; or a combination thereof.

42. The composition of any one of aspects 37 to 41, wherein theamine-functional silane comprises; from 40 wt % to 60 wt % of a primaryamine-functional silane; and from 40 wt % to 60 wt % of a secondaryamine-functional silane; wherein wt % is based on the total weight ofthe amine-functional silane in a composition.

43. The composition of any one of aspects 35 to 42, wherein theepoxy-functional reactive diluent comprises an epoxy-functional reactivediluent.

44. The composition of any one of aspects 35 to 43, wherein theepoxy-functional reactive diluent comprises a monoepoxide, apolyepoxide, or a combination of any of the foregoing

45. The composition of any one of aspects 35 to 44, wherein theepoxy-functional reactive diluent comprises an epoxy-functional reactivediluent characterized by a weight average molecular weight from 100Daltons to 1,000 Daltons, wherein the weight average molecular weight isdetermined by gel permeation chromatography, using a polystyrenestandard,

46. The composition of any one of aspects 35 to 45, wherein theepoxy-functional reactive diluent comprises a glycidyl ether.

47. The composition of any one of aspects 35 to 46, wherein theepoxy-functional reactive diluent comprises an aliphatic diglycidylether.

48. The composition of any one of aspects 1 to 47, comprising: from 50wt % to 70 wt % of the thiol-terminated polythioether prepolymer; from15 wt % to 21 wt % of the polyepoxide; from 2.5 wt % to 4.0 wt % of thelow density filler, wherein the low density filler is characterized by aspecific gravity within a range from 0.01 to 0.09, wherein the specificgravity is determined according to ASTM D1475; from 10 wt % to 16 wt %of an inorganic filler; from 1.8 wt % to 3.8 wt % of an adhesionpromoter; and from 0.2 wt % to 3 wt % of an epoxy-functional reactivediluent, wherein wt % is based on the total weight of the composition.

49. The composition of aspect 48, wherein, the polyepoxide comprises adiglycidyl ether of bisphenol A and a novolac epoxy resin, wherein thecomposition comprises: from 10 wt % to 25 wt % of the diglycidyl etherof bisphenol A; and from 0.2 wt % to 2 wt % of the novolac epoxy resin;and the adhesion promoter comprises a phenolic adhesion promoter and anamine-functional silane, wherein the composition comprises: from 1 wt %to 3 wt % of the phenolic adhesion promoter; and from 0.5 wt % to 2 wt %of the amine-functional silane; wherein wt % is based on the totalweight of the composition.

50. The composition of any one of aspects 48 and 49, wherein theamine-functional silane comprises a primary amine-functional silane anda secondary amine-functional, wherein the composition comprises: from0.4 wt % to 0.9 wt % of the primary amine-functional silane; and from0.4 wt % to 0.9 wt % of the secondary amine-functional silane, whereinwt % is based on the total weight of the composition.

51. The composition of any one of aspects 1 to 47, comprising: from 50wt % to 70 wt % of the thiol-terminated polythioether prepolymer; from15 wt % to 21 wt % of the polyepoxide, wherein the polyepoxide comprisesa diglycidyl ether of bisphenol A and a novolac epoxy resin, wherein thecomposition comprises: from 10 wt % to 25 wt % of the diglycidyl etherof bisphenol A, wherein the diglycidyl ether of bisphenol A comprisespendent hydroxyl groups; and from 0.2 wt % to 2 wt % of the novolacepoxy resin; from 2.5 wt % to 4.0 wt % of the low density filler,wherein the low density filler is characterized by a specific gravitywithin a range from 0.01 to 0.09, wherein the specific gravity isdetermined according to ASTM D1475; from 10 wt % to 16 wt % of theinorganic filler; from 1.8 wt % to 3.8 wt % of the adhesion promoter,wherein the adhesion promoter comprises a phenolic adhesion promoter andan amine-functional silane, wherein the composition comprises: from 1 wt% to 3 wt % of the phenolic adhesion promoter; and from 0.5 wt % to 2 wt% of the amine-functional silane; and from 0.2 wt % to 3 wt % of anepoxy-functional reactive diluent, wherein the epoxy-functional reactivediluent comprises an aliphatic diglycidyl ether, wherein wt % is basedon the total weight of the composition.

52. A cured sealant prepared using the composition of any one of aspects1 to 51.

53. The cured sealant of aspect 52, wherein the cured sealant exhibits apeel strength on Mil C-27725 and titanium C substrates of at least 25pli/100% CF (4.38 N/mm/100% CF) following immersion in Jet ReferenceFluid Type I for 120 days at 140° F. (60° C.), as determined accordingto AMS 3281.

54. The cured sealant of any one of aspects 52 to 53, wherein the curedsealant meets or exceeds the requirements for aerospace sealants as setforth in AMS 3277 and/or AMS 3281.

55. A part comprising the cured sealant of any one of aspects 52 to 54.

56. A method of sealing a part, comprising: applying the composition ofany one of aspects 1 to 52 to at least one surface of a part; and curingthe applied composition to seal the part.

57. A sealant system comprising a first component and a secondcomponent, wherein, the first component comprises: from 50 wt % to 70 wt% of a thiol-terminated polythioether; from 2.5 wt % to 4.0 wt % of alow density filler, wherein the low density filler is characterized by aspecific gravity within a range from 0.01 to 0.09, wherein the specificgravity is determined according to ASTM D1475, wherein wt % is based onthe total weight of the first component; and the second componentcomprises: from 75 wt % to 95 wt % of a polyepoxide, wherein wt % isbased on the total weight of the second component, wherein the firstcomponent and the second component combined provide the composition ofany one of aspects 1 to 52.

58. A cured sealant prepared using the system of aspect 57.

59. The cured sealant of aspect 58, wherein the cured sealant exhibits apeel strength on Mil C-27725 and titanium C substrates of at least 25pli/100% CF (4.38 N/mm/100% CF) following immersion in Jet ReferenceFluid Type I for 120 days at 140° F. (60° C.), as determined accordingto AMS 3281.

60. The cured sealant of any one of aspects 58 to 59, wherein the curedsealant meets or exceeds the requirements for aerospace sealants as setforth in AMS 3277 and/or AMS 3281.

61. A part comprising the cured sealant of any one of aspects 58 to 60.

62. A method of sealing a part, comprising: combining the firstcomponent and the second component of the sealant system of aspect 57 toprovide a curable sealant composition; applying the curable sealantcomposition to at least one surface of a part; and curing the appliedcurable sealant composition to seal the part.

1 A. A composition comprising: from 50 wt % to 70 wt % of athiol-terminated polythioether prepolymer; from 15 wt % to 21 wt % of apolyepoxide; and from 35 vol % to 55 vol % of a low density filler,wherein, the low density filler is characterized by a specific gravityless than 0.1; and the low density filler comprises low densitymicrocapsules comprise a coating of an aminoplast resin; wherein wt % isbased on the total weight of the composition, and vol % is based on thetotal volume of the composition, and wherein the composition ischaracterized by a specific gravity less than 0.9, wherein the specificgravity is determined according to ASTM D1475 (modified).

2A. The composition of aspect 1A, wherein when cured, the curedcomposition meets or exceeds the requirements for aerospace sealants asset forth in AMS 3277 and/or AMS 3281.

3 A. The composition of any one of aspects 1A to 2 A, wherein thecomposition is characterized by a specific gravity within a range from0.65 to 0.85, wherein the specific gravity is determined according toASTM D1475 (modified).

4A. The composition of any one of aspects 1A to 3A, wherein thethiol-terminated polythioether prepolymer comprises the chemicalstructure of Formula (1):

$\begin{matrix}{{–R}^{1}{–\left\lbrack {{{–S–}\left( {CH}_{2} \right)}_{2}{{–O–}\left\lbrack {{–R}^{2}{–O–}} \right\rbrack}_{m}{–\left( {CH}_{2} \right)}_{2}{–S–R}^{1}} \right\rbrack}_{n}–} & (1)\end{matrix}$

wherein,

-   -   each R¹ can independently comprise a C₂₋₁₀ n-alkanediyl group, a        C₃₋₆ branched alkanediyl group, a C₆₋₈ cycloalkanediyl group, a        C₆₋₁₀ alkanecycloalkanediyl group, a heterocyclic group, or a        —[(—CHR³—)_(p)—X—]_(q)—(CHR³)_(r)— group, wherein each R³ can        comprise from hydrogen or methyl;    -   each R² can independently comprise a C₂₋₁₀ n-alkanediyl group, a        C₃₋₆ branched alkanediyl group, a C₆₋₈ cycloalkanediyl group, a        C₆₋₁₄ alkanecycloalkanediyl group, a heterocyclic group, or a        —[(—CH₂-)_(p)—X—]_(q)—(CH₂)_(r)— group;    -   each X can independently comprise O, S, and —NR—, wherein R can        comprise from hydrogen or methyl;    -   m ranges from 0 to 50;    -   n is an integer ranging from 1 to 60;    -   p is an integer ranging from 2 to 6;    -   q is an integer ranging from 1 to 5; and    -   r is an integer ranging from 2 to 10.

5 A. The composition of any one of aspects 1A to 4 A, wherein the polyepoxide comprises: from 86 wt % to 99 wt % of a hydroxyl-functionaldiglycidyl ether of bisphenol A; and from 1 wt % to 11 wt % of a novolacpolyepoxide; wherein wt % is based on the total weight of thepolyepoxide in the composition.

6A. The composition of any one of aspects 1A to 5A, wherein thecomposition comprises: from 86 wt % to 99 wt % of a hydroxyl-functionaldifunctional polyepoxide; and from 1 wt % to 11 wt % of a trifunctionalpolyepoxide, wherein wt % is based on the total weight of thepolyepoxide in the composition.

7A. The composition of any one of aspects 1A to 6A, wherein thepolyepoxide comprises: from 86 wt % to 99 wt % of the diglycidyl etherof bisphenol A; and from 1 wt % to 11 wt % of the novolac epoxy resin,wherein wt % is based on the total weight of the polyepoxide in thecomposition.

8 A. The composition of any one of aspects 1A to 7 A, wherein, thecomposition comprises from 2.8 wt % to 4.0 wt % of the low densityfiller; and the aminoplast resin comprises a urea-formaldehyde resin;and the coated low density microcapsules are characterized by a specificgravity within a range from 0.03 to 0.06, wherein the specific gravityis determined according to ASTM D1475.

9A. The composition of any one of aspects 1A to 8A, further comprising:from 10 wt % to 16 wt % of an inorganic filler; from 1.8 wt % to 3.8 wt% of an adhesion promoter; and from 0.2 wt % to 3 wt % of anepoxy-functional reactive diluent, wherein wt % is based on the totalweight of the composition.

10A. The composition of aspect 9A, wherein the inorganic fillercomprises precipitated calcium carbonate, hydrated alumina, fumedsilica, calcium hydroxide, carbon black, or a combination off any of theforegoing.

11 A. The composition of aspect 9A, wherein the adhesion promotercomprises: from 45 wt % to 65 wt % of a phenolic adhesion promoter; andfrom 35 wt % to 55 wt % of an amine-functional silane, wherein wt % isbased on the total weight of the adhesion promoter in the composition.

12A. The composition of aspect 11A, wherein the amine-functional silanecomprises; from 40 wt % to 60 wt % of a primary amine-functional silane;and from 40 wt % to 60 wt % of a secondary amine-functional silane;wherein wt % is based on the total weight of the amine-functional silanein a composition.

13A. The composition of aspect 9A, wherein the epoxy-functional reactivediluent comprises an epoxy-functional reactive diluent characterized bya weight average molecular weight from 100 Daltons to 1,000 Daltons,wherein the weight average molecular weight is determined by gelpermeation chromatography, using a polystyrene standard,

14A. The composition of any one of aspects 1A to 13A, comprising: from50 wt % to 70 wt % of the thiol-terminated polythioether prepolymer;from 15 wt % to 21 wt % of the polyepoxide; from 2.5 wt % to 4.0 wt % ofthe low density filler, wherein the low density filler is characterizedby a specific gravity within a range from 0.01 to 0.09, wherein thespecific gravity is determined according to ASTM D1475; from 10 wt % to16 wt % of an inorganic filler; from 1.8 wt % to 3.8 wt % of an adhesionpromoter; and from 0.2 wt % to 3 wt % of an epoxy-functional reactivediluent, wherein wt % is based on the total weight of the composition.

15A. The composition of aspect 14A, wherein, the polyepoxide comprises adiglycidyl ether of bisphenol A and a novolac epoxy resin, wherein thecomposition comprises: from 10 wt % to 25 wt % of the diglycidyl etherof bisphenol A; and from 0.2 wt % to 2 wt % of the novolac epoxy resin;and the adhesion promoter comprises a phenolic adhesion promoter and anamine-functional silane, wherein the composition comprises: from 1 wt %to 3 wt % of the phenolic adhesion promoter; and from 0.5 wt % to 2 wt %of the amine-functional silane; wherein wt % is based on the totalweight of the composition.

16A. The composition of aspect 15A, wherein the amine-functional silanecomprises a primary amine-functional silane and a secondaryamine-functional, wherein the composition comprises: from 0.4 wt % to0.9 wt % of the primary amine-functional silane; and from 0.4 wt % to0.9 wt % of the secondary amine-functional silane, wherein wt % is basedon the total weight of the composition.

17A. The composition of of any one of aspects 1A to 16A, comprising from50 wt % to 70 wt % of the thiol-terminated polythioether prepolymer;from 15 wt % to 21 wt % of the polyepoxide, wherein the polyepoxidecomprises a diglycidyl ether of bisphenol A and a novolac epoxy resin,wherein the composition comprises: from 10 wt % to 25 wt % of thediglycidyl ether of bisphenol A, wherein the diglycidyl ether ofbisphenol A comprises pendent hydroxyl groups; and from 0.2 wt % to 2 wt% of the novolac epoxy resin; from 2.5 wt % to 4.0 wt % of the lowdensity filler, wherein the low density filler is characterized by aspecific gravity within a range from 0.01 to 0.09, wherein the specificgravity is determined according to ASTM D1475; from 10 wt % to 16 wt %of the inorganic filler; from 1.8 wt % to 3.8 wt % of the adhesionpromoter, wherein the adhesion promoter comprises a phenolic adhesionpromoter and an amine-functional silane, wherein the compositioncomprises: from 1 wt % to 3 wt % of the phenolic adhesion promoter; andfrom 0.5 wt % to 2 wt % of the amine-functional silane; and from 0.2 wt% to 3 wt % of an epoxy-functional reactive diluent, wherein theepoxy-functional reactive diluent comprises an aliphatic diglycidylether, wherein wt % is based on the total weight of the composition.

18A. A cured sealant prepared using the composition of any one ofaspects 1A to 17A.

19A. The cured sealant of aspect 18A, wherein the cured sealant meets orexceeds the requirements for aerospace sealants as set forth in AMS 3277and/or AMS 3281.

20A. A part comprising the cured sealant of aspect 18A.

21 A, A method of sealing a part, comprising: applying the compositionof any one of aspects 1A to 17A to at least one surface of a part; andcuring the applied composition to seal the part.

22A. A sealant system comprising a first component and a secondcomponent, wherein, the first component comprises: from 50 wt % to 70 wt% of a thiol-terminated polythioether; from 2.5 wt % to 4.0 wt % of alow density filler, wherein, the low density filler is characterized bya specific gravity within a range from 0.01 to 0.09, wherein thespecific gravity is determined according to ASTM D1475; and the lowdensity filler comprises low density microcapsules comprising a coatingof an aminoplast resin; wherein wt % is based on the total weight of thefirst component; and the second component comprises: from 75 wt % to 95wt % of a poly epoxide, wherein wt % is based on the total weight of thesecond component, wherein the first component and the second componentcombined provide the composition of claim 1.

Examples

Embodiments provided by the present disclosure are further illustratedby reference to the following examples, which describe compositions andsealants provided by the present disclosure. It will be apparent tothose skilled in the art that many modifications, both to materials, andto methods, may be practiced without departing from the scope of thedisclosure.

A sealant (Sealant 1) was prepared by combining and mixing Part A andPart B.

Part A was prepared in a suitable container by adding the componentslisted in Table 1, beginning with the thiol-terminated polythioetherprepolymers and phenolic adhesion promoters, then adding the calciumcarbonate and silica, followed by the silanes, catalyst and finally thelow density microcapsules.

TABLE 1 Part A formulation. Component Wt % Permapol ® P3.1e 76.39 76.39Thiol-terminated polythioether¹ Phenolic resin adhesion promoter² 1.141.14 Amine-functional silane 1.6 1.60 adhesion promoter³ Inorganicfiller⁴ 15.23 15.23 Catalyst⁵ .69 .69 Low density aminoplast-coated 3.963.96 microcapsules Plasticizer, solvent, additives 0.99 0.99 Total 100100 ¹Combination of Permapol P3.1e 2.2 (75.8 g) and Permapol 3.1e 2.8(0.91 g). ²Phenolic adhesion promoter (T-3920 and T-3921). ³Combiantionof primary aminosilane (0.8 g) and hindered silane (0.8 g). ⁴Combinationof precipitated CaCO₃, hydrated alumina, fumed silica, and calciumhydroxide. ⁵DABCO ®

The low density aminoplast-coated particles were prepared, as describedin U.S. Pat. No. 8,993,691, by combining a thermally expandedmicrocapsule such as Expancel® 091 DE 80 d30 (6 g; AkzoNobel),de-ionized water (551.8 g), and a melamine-formaldehyde resin (22.4 g;Cymel® 303; Cytec Industries Inc.). While stirring, a 10% para-toluenesulfonic acid solution (22.4 g; Sigma Aldrich) was added and the mixtureheated to 60° C. and held for 2 hours. After removing the heat, asaturated sodium bicarbonate solution (13 g) was added and the mixturestirred for 10 min. Solids were filtered using a Buchner funnel, rinsedwith distilled water, and allowed to dry at ambient temperature followedby drying for 24 hours at 49° C. The powder was sifted through a 250micron sieve. The aminoplast resin coated microparticles had a specificgravity from 0.05 to 0.06.

Part B was prepared by combining and mixing the components listed inTable 2.

TABLE 2 Part B formulation. Component Weight (g) Wt % PolyfunctionalEpoxy¹ 5.22 5.22 Hydroxyl-functional Difunctional Epoxy² 81.85 81.85Reactive diluent³ 4.97 4.97 Carbon black 0.44 0.44 Phenolic adhesionpromoter⁴ 3.01 3.01 Inorganic filler⁵ 4.5 4.50 Total 100 100 ¹Novolacepoxy resin. ²Hydroxyl-functional diglycidyl ether of bisphenol A.³Epoxy-functional reactive diluent. ⁴Phenolic adhesion promoter. ⁵Fumedsilica.

For the sealant composition incorporating the low densitymelamine-coated microcapsules (Sealant 1), 100 g of part A and 26 g ofpart B were mixed by hand or in a SpeedMixer-DAC 600 FVZ, and theuniformly mixed material was applied to a substrate cured in accordancewith AMS 3281.

The wt % for each of the components in the sealant compositionincorporated the low density melamine-coated filler is listed in Table3.

TABLE 3 Sealant Formulation combined Parts A and B. Component Wt %Permapol ® P3.1e 60.6 Thiol-terminated polythioether Phenolic adhesionpromoter 0.9 Amine-functional silane 1.3 adhesion promoter Inorganicfiller 13.0 Catalyst .55 Low density aminoplast-coated microcapsules 3.1Plasticizer, solvent, and additive 0.8 Polyfunctional epoxy 1.1Hydroxy-functional Difunctional Epoxy 16.9 Epoxy Reactive diluent 1.0Carbon black 0.1 Total 100

Two comparative sealant formulations were prepared.

Sealant 2 was similar to Sealant 1 except that the 3.96 wt % low densityaminoplast resin-coated microcapsules (specific gravity from 0.05 to0.06) in Part A were replaced with 2.04 wt % uncoated Expancel® 920 DE40D30 microcapsules (specific gravity about 0.03) (AkzoNobel).

Sealant 3 was similar to Sealant 1, except that the 5.25 wt % lowdensity aminoplast resin-coated microcapsules (specific gravity from0.05 to 0.06) in Part A were replaced with 1.70 wt % uncoated Expancel®920 DE80 D30 microcapsules (specific gravity about 0.03) (AkzoNobel).

For the sealant formulations incorporating lightweight Expancel® 920DE40 D30 and Expancel® 920 DE80 D30 microcapsules, 1.62 wt % and 1.35 wt% of the lightweight microcapsules was used, respectively. Theadjustment to the wt % of lightweight microcapsules was made so that thethree sealant formulations evaluated had a similar specific gravity ofabout 0.75 (0.73 to 0.77) (see Table 4). For the sealant formulationsincorporating Expancel® 920 DE40 D30, 100 g of part A was combined with26.77 g of part B. For sealant formulations incorporating Expancel® 920DE80 D30, per 100 g of part A were combined with 26.87 g of part B.

The formulations were applied to Mil C-27725, anodized aluminum,Alodine® 1200, stainless steel, and titanium C test substrates.

The dry adhesion following a 14-day cure at ambient temperature wasdetermined according to AMS 3181. Other measurements were made accordingto specification AMS-3281.

The results are presented in Table 4A and Table 4B.

TABLE 4A Properties of cured sealants. Test Method AMS 3281 ParagraphProperty Units Sealant 2 Sealant 3 Sealant 1 none Amount low wt %, basedon total 1.62 1.35 3.15 density filler weight none Amount low Estimatedvol %, based 39 34 43 density filler on total weight 3.6.2 ViscosityPoise 19,600 14,000 14,000 Pa-sec 1,960 ′1,400 1,400 3.6.5 Applicationg/min at 2 h 37 45 41 Time 3.6.8 Hardness Shore A in 24 h 35 33 353.6.12 Hydrolytic Shore A 38 38 41 stability 3.6.10 Specific gravity nounit 0.73 0.76 0.77 in hexane 3.6.17 Thermal at 300° F. 10 psi (149° didnot pass did not pass passed ruptures C., 1.03 MPa), 30 min, after fluidimmersion 3.6.22.1 Standard dry psi/% elongation 214/297 217/317 228/375cure MPa/% elongation 1.47/297  1.50/317  1.57 375

TABLE 4B Adhesion of cured sealants to various substrates. TestCondition Substrate Sealant 2 Sealant 3 Sealant 1 Dry Mil C-27725 43 pli39 pli 40 pli 14 days cure 100% CF 100% CF 100% CF Anodized 33 pli 38pli 40 pli 100% CF 100% CF 100% CF Alodine ® 1200 38 pli 45 pli 43 pli100% CF 100% CF 100% CF Stainless steel 51 pli 54 pli 51 pli 100% CF100% CF 100% CF Titanium C 44 pli 46 pli 52 pli 100% CF 100% CF 100% CF7 days at 140° F. (60° C.) in Mil C-27725 19/28 pli* 32/35 pli 46/53 pliJRF Type I/3% NaCl 100% CF 100% CF 100% CF Anodized 21/21 pli 25/27 pli37/41 pli 100% CF 100% CF 100% CF Alodine ® 1200 28/27 pli Noadhesion/30 pli 30/36 pli 100% CF 100% CF 100% CF Stainless steel 25/27pli 29/34 pli 42/40 pli 100% CF 100% CF 100% CF Titanium C 29/27 pli31/0 pli 52/40 pli 100% CF 100% CF 70 days at 140° F.(60° C.) in MilC-27725 22/23 pli 26/24 pli 32/32 pli JRF Type I/3% NaCl 100% CF 100% CF100% CF Titanium C 25/28 pli 25/25 pli 32/30 pli 100% CF 70% CF 100% CF120 days at 140° F. (60° C.) Mil C-27725 20 pli —* 33 pli in JRF Type Ionly 100% CF 100% CF on BMS-565-010 Titanium C 21 pli 21 pli 30 pli 100%CF 100% CF 100% CF on BMS-565-010 *Peel strength following immersion inJRF Type I was 19 pli (3.33 N/mm), with 100% cohesive failure; and thepeel strength following immersion in 3% NaCl was 28 pli (4.90 N/mm).

Each of the compositions in Table 4 have a vol % loading of low densitymicrocapsules between 30 vol % to 45 vol %, where vol % is based on thetotal volume of the composition, and had a similar specific gravity from0.73 to 0.77. Sealant 1 is estimated to have 43 vol % low densityfiller; Sealant 2, 39 vol % low density filler; and Sealant 3, 34 vol %low density filler.

As shown in Table 4, even with substantial reformulation of the sealantcomposition, sealant compositions comprising uncoated expandedthermoplastic microcapsules at loadings around 30 vol % to 40 vol %(1.62 wt % and 1.35 wt % for the compositions comprising Expancel® 920DE 40 D30 and Expancel® 920 DE80 ED30, respectively), exhibited asignificant decrease in the adhesion strength following exposure to JRFType I and 3% NaCl at high temperature.

Finally, it should be noted that there are alternative ways ofimplementing the embodiments disclosed herein. Accordingly, the presentembodiments are to be considered as illustrative and not restrictive.Furthermore, the claims are not to be limited to the details givenherein, and are entitled their full scope and equivalents thereof.

What is claimed is:
 1. A composition comprising: (a) a thiol-terminatedpolythioether prepolymer; (b) a curing agent comprising groups reactivewith thiol groups; and (c) from 35 vol % to 55 vol % of coatedlow-density thermoplastic microcapsules, wherein, the coated low-densitythermoplastic microcapsules comprise a coating of an aminoplast resin;the coated low-density thermoplastic microcapsules are characterized bya specific gravity less than 0.1; vol % is based on the total volume ofthe composition; and the composition is characterized by a specificgravity less than 0.9, wherein the specific gravity is determinedaccording to ASTM D1475 (modified).
 2. The composition of claim 1,wherein the thiol-terminated polythioether prepolymer comprises thechemical structure of Formula (1):—R¹—[—S—(CH₂)₂—O—[—R²—O-]_(m)—(CH₂)₂—S—R¹]_(n)—  (1) wherein, each R¹ isindependently selected from a C₂₋₁₀ n-alkanediyl group, a C₃₋₆ branchedalkanediyl group, a C₆₋₈ cycloalkanediyl group, a C₆₋₁₀alkanecycloalkanediyl group, a heterocyclic group, and a—[(—CHR³—)_(p)—X—]_(q)—(CHR³)_(r)— group, wherein each R³ isindependently selected from hydrogen and methyl; each R² isindependently selected from a C₂₋₁₀ n-alkanediyl group, a C₃₋₆ branchedalkanediyl group, a C₆₋₈ cycloalkanediyl group, a C₆₁₄alkanecycloalkanediyl group, a heterocyclic group, and a—[(—CH₂—)_(p)—X—]_(q)—(CH₂)_(r)— group; each X is independently selectedfrom O, S, and —NR—, wherein R is selected from hydrogen and methyl; mranges from 0 to 50; n is an integer ranging from 1 to 60; p is aninteger ranging from 2 to 6; q is an integer ranging from 1 to 5; and ris an integer ranging from 2 to
 10. 3. The composition of claim 1,wherein the groups reactive with thiol groups are selected from asMichael acceptor groups, alkenyl groups, and epoxide groups.
 4. Thecomposition of claim 1, wherein the composition comprises from 10 wt %to 30 wt % of the curing agent, wherein wt % is based on the totalweight of the composition.
 5. The composition of claim 1, wherein thecuring agent comprises a poly epoxide.
 6. The composition of claim 5,wherein the poly epoxide comprises a hydroxyl-functional difunctionalpolyepoxide and a trifunctional polyepoxide.
 7. The composition of claim5, wherein the polyepoxide comprises: from 86 wt % to 99 wt % of ahydroxyl-functional diglycidyl ether of bisphenol A; and from 1 wt % to11 wt % of a novolac polyepoxide; wherein wt % is based on the totalweight of the polyepoxide in the composition.
 8. The composition ofclaim 1, wherein the coated low-density thermoplastic microcapsules arecharacterized by a specific gravity within a range from 0.02 to 0.08,wherein the specific gravity is determined according to ASTM D1475. 9.The composition of claim 1, wherein the coated low-density thermoplasticmicrocapsules comprise coated thermally expanded thermoplasticmicrocapsules.
 10. The composition of claim 1, wherein the aminoplastresin comprises a melamine-formaldehyde resin.
 11. The composition ofclaim 1, wherein the aminoplast resin comprises a urea-formaldehyderesin.
 12. The composition of claim 1, wherein the composition comprisesfrom 2.6 wt % to 4.0 wt % of the coated low-density thermoplasticmicrocapsules, wherein wt % is based on the total weight of thecomposition.
 13. The composition of claim 1, wherein the composition ischaracterized by a specific gravity within a range from 0.65 to 0.85,wherein the specific gravity is determined according to ASTM D1475(modified).
 14. The composition of claim 1, further comprising: from 10wt % to 16 wt % of an inorganic filler; from 1.8 wt % to 3.8 wt % of anadhesion promoter; and from 0.2 wt % to 3 wt % of an epoxy-functionalreactive diluent; wherein wt % is based on the total weight of thecomposition
 15. The composition of claim 14, wherein the adhesionpromoter comprises: from 45 wt % to 65 wt % of a phenolic adhesionpromoter; and from 35 wt % to 55 wt % of an amine-functional silane,wherein wt % is based on the total weight of the adhesion promoter inthe composition.
 16. The composition of claim 15, wherein theamine-functional silane comprises; from 40 wt % to 60 wt % of a primaryamine-functional silane; and from 40 wt % to 60 wt % of a secondaryamine-functional silane; wherein wt % is based on the total weight ofthe amine-functional silane in a composition.
 17. A cured sealantprepared using the composition of claim
 1. 18. The cured sealant ofclaim 17, wherein the cured sealant meets or exceeds the requirementsfor aerospace sealants as set forth in AMS 3277 and/or AMS
 3281. 19. Apart comprising the cured sealant of claim
 17. 20. The part of claim 19,wherein the part is an aerospace part.
 21. A method of sealing a part,comprising: applying the composition of claim 1 to at least one surfaceof a part; and curing the applied composition to seal the part.
 22. Asealed part prepared using the method of claim
 21. 23. A sealant systemfor preparing the composition of claim 1, wherein the sealant systemcomprises a first component and a second component, wherein, the firstcomponent comprises the polythioether; the second component comprisesthe curing agent; and the first component, the second component, or boththe first and second components comprise the coated low-densitythermoplastic microcapsules.